Parent Holding Company Information (Condensed) - Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities
Net income	$ 81,860	$ 77,757	$ 63,444	$ 43,339	$ 57,410	$ 51,610	$ 52,392	$ 49,132	$ 266,400	$ 210,544	$ 181,878
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation, net of tax benefits									3,629	7,475	3,122
Net cash provided by operating activities									189,545	226,649	280,711
Investing Activities
Net additions of premises and equipment									(11,717)	(16,398)	(18,637)
Net cash used in investing activities									(3,563,696)	(42,682)	(872,420)
Financing Activities
Net decrease in other borrowed funds									564	14,109	(5,059)
Cash dividends paid									(131,263)	(124,468)	(85,493)
Tax withholding payments for stock-based compensation									(1,082)	(1,293)	(1,214)
Proceeds from stock option exercises									993	2,896	24
Net cash provided by (used in) financing activities									3,676,332	(56,796)	595,495
Net increase in cash, cash equivalents and restricted cash									302,181	127,171	3,786
Cash, cash equivalents and restricted cash at beginning of period				330,961				203,790	330,961	203,790	200,004
Cash, cash equivalents and restricted cash at end of period	633,142				330,961				633,142	330,961	203,790
Parent Company
Operating Activities
Net income									266,400	210,544	181,878
Adjustments to reconcile net income to net cash provided by operating activities:
Subsidiary income in excess of dividends distributed									(87,703)	(83,806)	(39,798)
Stock-based compensation, net of tax benefits									1,216	1,320	1,219
Net change in other assets and other liabilities									(7,222)	1,854	(3,209)
Net cash provided by operating activities									172,691	129,912	140,090
Investing Activities
Net additions of premises and equipment									(111)	(114)	(300)
Proceeds from sale of marketable equity securities									0	89	0
Equity contributions to subsidiaries									(13,638)	(13,485)	(24,989)
Net cash used in investing activities									(13,749)	(13,510)	(25,289)
Financing Activities
Net decrease in other borrowed funds									0	0	(11,543)
Cash dividends paid									(131,263)	(124,468)	(85,493)
Tax withholding payments for stock-based compensation									(1,082)	(1,293)	(1,214)
Proceeds from stock option exercises									993	2,896	24
Net cash provided by (used in) financing activities									(131,352)	(122,865)	(98,226)
Net increase in cash, cash equivalents and restricted cash									27,590	(6,463)	16,575
Cash, cash equivalents and restricted cash at beginning of period				$ 57,836				$ 64,299	57,836	64,299	47,724
Cash, cash equivalents and restricted cash at end of period	$ 85,426				$ 57,836				$ 85,426	$ 57,836	$ 64,299