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	$ 51,705	$ 62,964	$ 74,345	$ 119,240
Change in debt securities available-for-sale:
Unrealized holding gains (losses) for the period	15,728	51,249	119,682	113,514
Reclassification adjustment for securities (gains) losses realized in income	(511)	(1,165)	(5,685)	(1,062)
Income tax effect	(2,906)	(11,825)	(25,317)	(26,403)
Unrealized gains (losses) on available-for-sale debt securities	12,311	38,259	88,680	86,049
Change in securities held-to-maturity:
Amortization of unrealized losses on securities transferred from available-for-sale	0	564	0	1,021
Income tax effect	0	(129)	0	(235)
Changes from securities held-to-maturity	0	435	0	786
Cash flow hedges:
Net unrealized derivative gains (losses) on cash flow hedges	(246)	944	7,557	552
Reclassification adjustment for (gains) losses realized in net income	(1,670)	(6)	(2,101)	(391)
Income tax effect	470	(231)	(1,341)	(40)
Changes from cash flow hedges	(1,446)	707	4,115	121
Defined benefit pension plans:
Amortization of net loss recognized in income	27	21	54	41
Income tax effect	(6)	(5)	(13)	(10)
Changes from defined benefit pension plans	21	16	41	31
Other comprehensive income (loss), net of tax	10,886	39,417	92,836	86,987
Comprehensive income	$ 62,591	$ 102,381	$ 167,181	$ 206,227