Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
AOCI Attributable to Parent, Net of Tax
Balance, beginning	$ 2,353,955	$ 2,203,715	$ 2,307,041	$ 1,960,733
Other comprehensive income (loss) before reclassifications			(63,109)	91,630
Reclassification adjustments for gains included in net income (loss)				(758)
Total other comprehensive (loss) income, net of tax	(12,783)	1,189	(65,431)	90,872
Balance, ending	2,387,616	2,255,089	2,387,616	2,255,089
Gains (Losses) on Available-For-Sale and Transferred Debt Securities
AOCI Attributable to Parent, Net of Tax
Balance, beginning			143,443	40,226
Other comprehensive income (loss) before reclassifications			(63,468)	92,027
Reclassification adjustments for gains included in net income (loss)				(758)
Total other comprehensive (loss) income, net of tax			(65,790)	91,269
Balance, ending	77,653	131,495	77,653	131,495
(Losses) Gains on Derivatives Used for Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax
Balance, beginning			(353)	0
Other comprehensive income (loss) before reclassifications			359	(397)
Reclassification adjustments for gains included in net income (loss)				0
Total other comprehensive (loss) income, net of tax			359	(397)
Balance, ending	6	(397)	6	(397)
Reclassification adjustments for gains and transfers included in net income
AOCI Attributable to Parent, Net of Tax
Reclassification adjustments for gains included in net income (loss)			650
Reclassification adjustments for amortization included in net income for transferred securities
AOCI Attributable to Parent, Net of Tax
Reclassification adjustments for gains included in net income (loss)			1,672
Accumulated Other Compre- hensive Income (loss)
AOCI Attributable to Parent, Net of Tax
Balance, beginning	90,442	129,909	143,090	40,226
Total other comprehensive (loss) income, net of tax	(12,783)	1,189	(65,431)	90,872
Balance, ending	$ 77,659	$ 131,098	$ 77,659	$ 131,098