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Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Consolidated Statements of Comprehensive Income [Abstract] |  |  |
Net income | $ 106,521 | $ 95,636 | $ 86,795
Investment securities available-for-sale: |  |  |
Change in net unrealized gains (losses) during the period | (6,545) | (19,379) | 3,151
Reclassification adjustment for net gains included in income | (718) | (330) | (137)
Change in unamortized loss on available-for-sale investment securities transferred into held-to-maturity | 1,858 | 1,858 | 1,611
Change in net unrealized gain (loss) on derivatives | (1,095) | (203) | 165
Reclassification adjustment for derivative net (gains) losses included in net income | 1,132 | 0 | 0
Defined benefit post-retirement benefit plans: |  |  |
Change in net actuarial loss | (1,264) | 3,983 | 58
Other comprehensive income (loss), before tax | (6,632) | (14,071) | 4,848
Deferred tax benefit (expense) related to other comprehensive income (loss) | 2,797 | 5,537 | (1,908)
Other comprehensive income (loss), net of tax | (3,835) | (8,534) | 2,940
Comprehensive income | $ 102,686 | $ 87,102 | $ 89,735

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- Definition Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e557-108580 + Details
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- Definition Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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