Condensed Financial Information - Parent Company Only Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flows From Operating Activities:
Net Income	$ 178,040	$ 226,339	$ 208,393
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities [Abstract]
Amortization of issuance costs and discounts on long-term borrowings	1,128	842	813
Stock-based compensation	7,529	7,413	7,965
(Decrease) increase in other liabilities and payable to non-bank subsidiaries	(110,781)	(195,903)	(31,153)
Total adjustments	(23,552)	(98,626)	88,427
Net cash provided by operating activities	154,488	127,713	296,820
Cash Flows From Investing Activities
Net cash used in investing activities	(2,499,480)	(893,346)	(740,717)
Cash Flows From Financing Activities:
Repayments of long-term borrowings	(82,533)	(596,056)	(100,165)
Proceeds from long-term borrowings	495,898	485,000	50,000
Net proceeds from issuance of preferred stock	192,878	0	0
Net proceeds from issuance of common stock	7,375	6,362	6,735
Dividends paid	(90,957)	(92,330)	(89,654)
Acquisition of treasury stock	(39,748)	(111,457)	(95,308)
Net cash provided by financing activities	3,675,033	837,737	487,488
Parent
Cash Flows From Operating Activities:
Net Income	178,040	226,339	208,393
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities [Abstract]
Amortization of issuance costs and discounts on long-term borrowings	1,128	842	813
Stock-based compensation	7,529	7,413	7,967
(Increase) decrease in other assets	(307,976)	(20,449)	6,327
Equity in undistributed net income of subsidiaries	(55,895)	(38,400)	(73,460)
(Decrease) increase in other liabilities and payable to non-bank subsidiaries	(244,598)	1,580	36,273
Total adjustments	(599,812)	(49,014)	(22,080)
Net cash provided by operating activities	(421,772)	177,325	186,313
Cash Flows From Investing Activities
Net cash used in investing activities	0	0	0
Cash Flows From Financing Activities:
Repayments of long-term borrowings	(19,453)	0	0
Proceeds from long-term borrowings	370,898	0	0
Net proceeds from issuance of preferred stock	192,878	0	0
Net proceeds from issuance of common stock	7,375	6,362	6,733
Dividends paid	(90,956)	(92,330)	(89,654)
Acquisition of treasury stock	(39,748)	(111,457)	(95,308)
Net cash provided by financing activities	420,994	(197,425)	(178,229)
Net (Decrease) Increase in Cash and Cash Equivalents	(778)	(20,100)	8,084
Cash and Cash Equivalents at Beginning of Year	10,841	30,941	22,857
Cash and Cash Equivalents at End of Year	$ 10,063	$ 10,841	$ 30,941