Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 50,792	$ 96,460	$ 64,939	$ 197,897
Other comprehensive income, before tax:
Change in unrealized holding gains on securities available for sale	29,356	64,176	78,111	139,506
Unrealized (loss) on transfer of securities held to maturity to available for sale	0	0	0	(11,813)
Reclassification adjustment for net realized (gains) losses included in net income	(485)	528	(8,896)	13,712
Accretion of net unrealized loss on securities transferred to held to maturity	59	122	156	2,539
Change in the actuarial loss of defined benefit plan and post-retirement benefit plans	76	66	(2,492)	2,949
Total other comprehensive income, before tax	29,006	64,892	66,879	146,893
Deferred tax (expense) related to other comprehensive income	(8,017)	(17,936)	(18,485)	(40,602)
Other comprehensive income, net of tax	20,989	46,956	48,394	106,291
Comprehensive income	$ 71,781	$ 143,416	$ 113,333	$ 304,188