Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net Income	$ 226,339	$ 208,393	$ 171,753
Unrealized gains (losses) on available for sale investment securities:
Unrealized gain (loss) on securities	56,919	(24,326)	10,432
Reclassification adjustment for securities gains included in net income	(3,686)	(30)	(5,894)
Amortization of net unrealized losses on securities transferred to held to maturity	6,285	2,098	0
Non-credit related unrealized (loss) gain on other-than-temporarily impaired debt securities	(680)	222	185
Net unrealized gains (losses) on available for sale investment securities	58,838	(22,036)	4,723
Defined benefit pension plan and postretirement benefits:
Unrecognized pension and postretirement (cost) income	(937)	1,400	(609)
Amortization of net unrecognized pension and postretirement income	1,025	1,648	1,361
Net unrealized gains on defined benefit pension and postretirement plans	88	3,048	752
Other Comprehensive Income (Loss)	58,926	(18,988)	5,475
Total Comprehensive Income	$ 285,265	$ 189,405	$ 177,228

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.

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