Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 62,942	$ 71,596
Other comprehensive income (loss), net of tax:
Unrealized holding gains (losses) on securities carried at fair value arising during the period	37,444	(27,606)
Reclassification adjustment for gains included in net income	(87)	0
Tax effect	(7,845)	5,797
Net unrealized gains (losses) on securities carried at fair value, net of tax	29,512	(21,809)
Unrealized gains (losses) on interest rate swaps designated as cash flow hedges	(7,552)	7,963
Reclassification adjustment for (gains) losses included in net income	(1,288)	242
Tax effect	1,856	(1,723)
Net unrealized (losses) gains on interest rate swaps designated as cash flow hedges, net of tax	(6,984)	6,482
Adjustment for pension and other postretirement benefits	95	142
Tax effect	(20)	(30)
Net adjustment for pension and other postretirement benefits	75	112
Other comprehensive income (loss), net of tax	22,603	(15,215)
Total comprehensive income, net of tax	$ 85,545	$ 56,381