Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 69,781	$ 51,348	$ 189,021	$ 143,332
Change in debt securities available-for-sale:
Unrealized holding gains (losses) for the period	19,567	(18,159)	133,081	(51,280)
Reclassification for securities transferred to held-to-maturity	0	0	0	14,007
Reclassification adjustment for securities (gains) losses realized in income	(424)	(135)	(1,486)	(2,417)
Income tax effect	(3,602)	4,188	(30,005)	9,368
Unrealized gains (losses) on available-for-sale debt securities	15,541	(14,106)	101,590	(30,322)
Change in securities held-to-maturity:
Adjustment for securities transferred to available-for-sale	0	0	0	19,412
Adjustment for securities transferred from available-for-sale	0	0	0	(14,007)
Amortization of unrealized losses on securities transferred from available-for-sale	1,384	628	2,405	1,740
Income tax effect	(392)	(146)	(627)	(1,291)
Changes from securities held-to-maturity	992	482	1,778	5,854
Cash flow hedges:
Net unrealized derivative gains (losses) on cash flow hedges	(73)	725	479	6,804
Reclassification adjustment for (gains) losses realized in net income	(21)	(226)	(412)	553
Income tax effect	23	(122)	(17)	(1,805)
Changes from cash flow hedges	(71)	377	50	5,552
Defined benefit pension plans:
Amortization of net loss recognized in income	20	27	61	81
Income tax effect	(5)	(7)	(15)	(20)
Changes from defined benefit pension plans	15	20	46	61
Other comprehensive income (loss), net of tax	16,477	(13,227)	103,464	(18,855)
Comprehensive income	$ 86,258	$ 38,121	$ 292,485	$ 124,477