Condensed Financial Information - Parent Company Only Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flows From Operating Activities:
Net Income	$ 226,339	$ 208,393	$ 171,753
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities [Abstract]
Amortization of issuance costs and discounts on long-term debt	842	813	845
Stock-based compensation	7,413	7,965	5,209
Increase in other liabilities and payable to non-bank subsidiaries	(195,903)	(31,153)	(17,369)
Total adjustments	(98,626)	88,427	116,005
Net cash provided by operating activities	127,713	296,820	287,758
Cash Flows From Investing Activities
Net cash used in investing activities	(893,346)	(740,717)	(1,135,331)
Cash Flows From Financing Activities:
Repayments of long-term debt	(596,056)	(100,165)	(115,153)
Additions to long-term debt	485,000	50,000	223,251
Net proceeds from issuance of common stock	6,362	6,735	8,538
Dividends paid	(92,330)	(89,654)	(80,368)
Acquisition of treasury stock	(111,457)	(95,308)	0
Net cash provided by financing activities	837,737	487,488	897,143
Parent
Cash Flows From Operating Activities:
Net Income	226,339	208,393	171,753
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities [Abstract]
Amortization of issuance costs and discounts on long-term debt	842	813	845
Stock-based compensation	7,413	7,967	4,740
(Increase) decrease in other assets	(20,449)	6,327	(17,882)
Equity in undistributed net income of subsidiaries	(38,400)	(73,460)	(128,298)
Increase in other liabilities and payable to non-bank subsidiaries	1,580	36,273	31,241
Total adjustments	(49,014)	(22,080)	(109,354)
Net cash provided by operating activities	177,325	186,313	62,399
Cash Flows From Investing Activities
Net cash used in investing activities	0	0	0
Cash Flows From Financing Activities:
Repayments of long-term debt	0	0	(100,000)
Additions to long-term debt	0	0	123,251
Net proceeds from issuance of common stock	6,362	6,733	9,007
Dividends paid	(92,330)	(89,654)	(80,368)
Acquisition of treasury stock	(111,457)	(95,308)	0
Net cash provided by financing activities	(197,425)	(178,229)	(48,110)
Net (Decrease) Increase in Cash and Cash Equivalents	(20,100)	8,084	14,289
Cash and Cash Equivalents at Beginning of Year	30,941	22,857	8,568
Cash and Cash Equivalents at End of Year	$ 10,841	$ 30,941	$ 22,857