Parent Holding Company Information (Condensed) - Condensed Statements of Operations and Comprehensive Income (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
Expenses
Compensation and employee benefits									$ 253,047	$ 222,753	$ 195,056
Other operating expenses									66,809	62,775	54,294
Total non-interest expense	$ 111,187	$ 103,373	$ 94,764	$ 95,487	$ 95,252	$ 110,675	$ 86,170	$ 82,830	404,811	374,927	320,127
Income tax benefit	(18,950)	(18,754)	(14,306)	(9,630)	(12,203)	(12,212)	(12,568)	(11,667)	(61,640)	(48,650)	(40,331)
Net Income	$ 81,860	$ 77,757	$ 63,444	$ 43,339	$ 57,410	$ 51,610	$ 52,392	$ 49,132	266,400	210,544	181,878
Comprehensive Income									369,264	260,197	174,430
Parent Company
Income
Dividends from subsidiaries									188,000	142,000	153,574
Intercompany charges for services									2,332	20,661	16,523
Other income									954	513	1,284
Total income									191,286	163,174	171,381
Expenses
Compensation and employee benefits									5,646	25,806	20,873
Other operating expenses									10,051	15,118	12,201
Total non-interest expense									15,697	40,924	33,074
Income before income tax benefit and equity in undistributed net income of subsidiaries									175,589	122,250	138,307
Income tax benefit									3,108	4,488	3,773
Income before equity in undistributed net income of subsidiaries									178,697	126,738	142,080
Equity in undistributed net income of subsidiaries									87,703	83,806	39,798
Net Income									266,400	210,544	181,878
Comprehensive Income									$ 369,264	$ 260,197	$ 174,430