Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 147,316	$ 57,169
Unrealized (losses) gains on securities available for sale:
Unrealized (losses) gains on securities available for sale arising during the period	(56,501)	144,843
Tax effect	12,995	(33,313)
Reclassification adjustment for realized gains on securities available for sale included in income before income taxes	(9,207)	(19,795)
Tax effect	2,118	4,553
Total change in unrealized (losses) gains on securities available for sale, net of tax	(50,595)	96,288
Unrealized losses on securities available for sale transferred to held to maturity:
Reclassification adjustment for accretion of unrealized losses on securities available for sale transferred to held to maturity	(475)	0
Tax effect	109	0
Total change in unrealized losses on securities available for sale transferred to held to maturity, net of tax	(366)	0
Change in pension obligation:
Amortization of actuarial losses	6,529	6,264
Tax effect	(1,502)	(1,441)
Total change in pension obligation, net of tax	5,027	4,823
Net current period other comprehensive (loss) income	(45,934)	101,111
Total comprehensive income	$ 101,382	$ 158,280