Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
AOCI Attributable to Parent, Net of Tax
Balance, beginning	$ 2,295,385	$ 2,136,644	$ 2,307,041	$ 1,960,733
Other comprehensive income before reclassifications			(51,728)	90,422
Reclassification adjustments for gains included in net income				(739)
Total other comprehensive income (loss), net of tax	10,522	30,185	(52,648)	89,683
Balance, ending	2,353,955	2,203,715	2,353,955	2,203,715
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 before reclassifications			(52,064)	90,763
Reclassification adjustments for gains included in net income				(739)
Total other comprehensive income (loss), net of tax			(52,984)	90,024
Balance, ending	90,459	130,250	90,459	130,250
(Losses) Gains on Derivatives Used for Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax
Balance, beginning			(353)	0
Other comprehensive income before reclassifications			336	(341)
Reclassification adjustments for gains included in net income				0
Total other comprehensive income (loss), net of tax			336	(341)
Balance, ending	(17)	(341)	(17)	(341)
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			278
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			642
Accumulated Other Compre- hensive Income
AOCI Attributable to Parent, Net of Tax
Balance, beginning	79,920	99,724	143,090	40,226
Total other comprehensive income (loss), net of tax	10,522	30,185	(52,648)	89,683
Balance, ending	$ 90,442	$ 129,909	$ 90,442	$ 129,909