Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 226,409	$ 238,206	$ 190,830
Change in debt securities available-for-sale:
Unrealized holding gains (losses) for the period	125,214	123,006	(4,769)
Reclassification for securities transferred to held-to-maturity	0	0	14,007
Reclassification adjustment for securities (gains) losses realized in income	(10,767)	(1,923)	(2,060)
Income tax effect	(25,243)	(27,604)	(1,386)
Unrealized gains (losses) on available-for-sale debt securities	89,204	93,479	5,792
Change in securities held-to-maturity:
Adjustment for securities transferred to available-for-sale	0	8,200	19,412
Adjustment for securities transferred from available-for-sale	0	0	(14,007)
Amortization of unrealized losses on securities transferred     from available-for-sale	0	2,812	2,181
Income tax effect	0	(2,497)	(1,394)
Changes from securities held-to-maturity	0	8,515	6,192
Cash flow hedges:
Net unrealized derivative gains (losses) on cash flow hedges	8,261	(543)
Net unrealized derivative gains (losses) on cash flow hedges			5,145
Reclassification adjustment for (gains) losses realized in net income	(5,153)	(596)
Reclassification adjustment for (gains) losses realized in net income			150
Income tax effect	(764)	280
Income tax effect			(1,298)
Changes from cash flow hedges	2,344	(859)
Changes from cash flow hedges			3,997
Defined benefit pension plans:
Amortization of net loss recognized in income	21	30	191
Income tax effect	(5)	(8)	(47)
Changes from defined benefit pension plans	16	22	144
Other comprehensive income (loss)	91,564	101,157	16,125
Comprehensive income	$ 317,973	$ 339,363	$ 206,955