Shareholders' Equity and Other Comprehensive Income (OCI) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Beginning balance	$ 4,941,690	$ 3,133,602	$ 2,961,566
Other comprehensive income (loss) before reclassifications	153,993	154,442	(33,057)
Amounts reclassified from accumulated other comprehensive income (loss)	(60,999)	(5,619)	862
Net current period other comprehensive income (loss)	92,994	160,061	(32,195)
Reclassification from adoption of ASU 2018-02			0
Ending balance	5,161,334	4,941,690	3,133,602
Accumulated other comprehensive income, net	158,635	65,641
Net Unrealized Gains (Losses) on Cash Flow Hedges(1)
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Beginning balance	(18,487)	(12,137)	(12,137)
Other comprehensive income (loss) before reclassifications	73,502	(6,350)	0
Amounts reclassified from accumulated other comprehensive income (loss)	(2,049)	0	0
Net current period other comprehensive income (loss)	71,453	(6,350)	0
Reclassification from adoption of ASU 2018-02			0
Cumulative-effect adjustment from adoption of ASU 2016-01			0
Ending balance	52,966	(18,487)	(12,137)
Net Unrealized Gains (Losses) on Investment Securities Available for Sale(1)
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Beginning balance	83,666	(83,179)	(43,470)
Other comprehensive income (loss) before reclassifications	80,491	161,170	(33,023)
Amounts reclassified from accumulated other comprehensive income (loss)	(58,488)	5,675	960
Net current period other comprehensive income (loss)	22,003	166,845	(32,063)
Reclassification from adoption of ASU 2018-02			(7,763)
Cumulative-effect adjustment from adoption of ASU 2016-01			117
Ending balance	105,669	83,666	(83,179)
Post-Retirement Unfunded Health Benefit
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Beginning balance	462	896	853
Other comprehensive income (loss) before reclassifications	0	(378)	(34)
Amounts reclassified from accumulated other comprehensive income (loss)	(462)	(56)	(98)
Net current period other comprehensive income (loss)	(462)	(434)	(132)
Reclassification from adoption of ASU 2018-02			175
Cumulative-effect adjustment from adoption of ASU 2016-01			0
Ending balance	0	462	896
AOCI
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Beginning balance	65,641	(94,420)	(54,754)
Net current period other comprehensive income (loss)	92,994	160,061	(32,195)
Reclassification from adoption of ASU 2018-02			(7,588)
Cumulative-effect adjustment from adoption of ASU 2016-01			117
Ending balance	158,635	$ 65,641	$ (94,420)
Valuation Allowance of Deferred Tax Assets | Net Unrealized Gains (Losses) on Investment Securities Available for Sale(1)
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Accumulated other comprehensive income, net	(13,300)
Valuation Allowance of Deferred Tax Assets | Net Unrealized Gains (Losses) on Cash Flow Hedges
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Accumulated other comprehensive income, net	$ (12,100)