pre_text: ADVANCED ENERGY INDUSTRIES, INC. NOTES TO CONSOLIDATED FINANCIAL STATEMENTS – (continued) (in thousands, except per share amounts) Deferred tax assets and liabilities are recognized for the future tax consequences of differences between the carrying amounts of assets and liabilities and their respective tax bases using enacted tax rates in effect for the year in which the differences are expected to be reversed. Significant deferred tax assets and liabilities consist of the following: Of the $32.7 million and $40.2 million net deferred tax asset at December 31, 2019 and 2018, respectively, $42.7 million and $47.1 million is reflected as a net non-current deferred tax asset and $10.0 million and $7.0 million is reflected as a long-term liability at December 31, 2019 and 2018, respectively. As of December 31, 2019, the Company has recorded a valuation allowance on $16.0 million of its U.S. domestic deferred tax assets, largely attributable to acquired federal capital loss carryforwards for which the Company does not have sufficient income in the character to realize that attribute, and state carryforward attributes that are expected to expire before sufficient income can be realized in those jurisdictions. The remaining valuation allowance on deferred tax assets approximates $60.2 million and is associated primarily with operations in Austria, Germany, Hong Kong and Switzerland. As of December 31, 2019, there is not sufficient positive evidence to conclude that such deferred tax assets, presently reduced by a valuation allowance, will be recognized. The December 31, 2019 valuation allowance balance reflects an increase of $45.3 million during the year. The change in the valuation allowance is primarily due to increases from acquired Artesyn positions and current year activity, partially offset by decreases due to foreign exchange movements
table: Years Ended December 31,
table: 2019 2018
table: Deferred tax assets
table: Stock based compensation $1,757 $1,337
table: Net operating loss and tax credit carryforwards 86,879 38,622
table: Interest expense limitation 7,620 —
table: Pension obligation 13,473 3,302
table: Excess and obsolete inventory 3,217 2,161
table: Deferred revenue 3,305 6,903
table: Employee bonuses and commissions 2,537 1,874
table: Depreciation and amortization 29,015 29,525
table: Operating lease liabilities 23,451 —
table: Other 9,685 9,961
table: Deferred tax assets 180,939 93,685
table: Less: Valuation allowance (76,206) (30,924)
table: Net deferred tax assets 104,733 62,761
table: Deferred tax liabilities
table: Depreciation and amortization 41,549 17,723
table: Unremitted earnings 4,740 3,529
table: Operating lease right-of-use assets 22,774 —
table: Other 2,966 1,267
table: Deferred tax liabilities 72,029 22,519
table: Net deferred tax assets $32,704 $40,242
question: Analyse this data from a financial earnings document. What was the change in pension obligation between 2018 and 2019?