Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 238,206	$ 190,830	$ 95,725
Change in debt securities available-for-sale:
Unrealized holding gains (losses) for the period	123,006	(4,769)	14,259
Reclassification for securities transferred to held-to-maturity		14,007
Reclassification adjustment for securities gains realized in income	(1,923)	(2,060)	(9,135)
Income tax effect	(27,604)	(1,386)	(1,669)
Unrealized gains (losses) on available-for-sale debt securities	93,479	5,792	3,455
Change in securities held-to-maturity:
Adjustment for securities transferred to available-for-sale	8,200	19,412
Adjustment for securities transferred from available-for-sale		(14,007)
Amortization of unrealized losses on securities transferred from available-for-sale	2,812	2,181	1,830
Income tax effect	(2,497)	(1,394)	(627)
Changes from securities held-to-maturity	8,515	6,192	1,203
Cash flow hedges:
Net unrealized derivative gains (losses) on cash flow hedges	(543)	5,145	927
Reclassification adjustment for (gains) losses realized in net income	(596)	150	6,135
Income tax effect	280	(1,298)	(2,684)
Changes from cash flow hedges	(859)	3,997	4,378
Defined benefit pension plans:
Amortization of net loss recognized in income	30	191	159
Income tax effect	(8)	(47)	(95)
Changes from defined benefit pension plans	22	144	64
Other comprehensive income (loss), net of tax	101,157	16,125	9,100
Comprehensive income	$ 339,363	$ 206,955	$ 104,825