Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 284,020	$ 149,523	$ 108,032
Other comprehensive income (loss), net of tax:
Unrealized holding gains (losses) on securities carried at fair value arising during the period	(34,054)	1,269	(18,723)
Reclassification adjustment for (gains) losses on realized income	(224)	7,388	(129)
Tax effect	7,198	(3,029)	6,598
Net unrealized gains (losses) on securities carried at fair value, net of tax	(27,080)	5,628	(12,254)
Unrealized gains on interest rate swaps designated as cash flow hedges	2,841	4,263	0
Reclassification adjustment for (gains) losses included in net income	(1,871)	1,633	0
Tax effect	(203)	(2,064)	0
Net unrealized gains on interest rate swaps designated as cash flow hedges, net of tax	767	3,832	0
Plan remeasurement	0	13,011	(707)
Adjustment for pension and other postretirement benefits	(11,339)	1,752	2,630
Tax effect	2,381	(5,167)	(673)
Net adjustment for pension and other postretirement benefits	(8,958)	9,596	1,250
Other comprehensive income (loss), net of tax	(35,271)	19,056	(11,004)
Total comprehensive income, net of tax	$ 248,749	$ 168,579	$ 97,028