Parent Company Financial Information - STATEMENTS OF OPERATIONS (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
Expense
Subordinated debentures									$ 20,647	$ 10,680	$ 6,716
Compensation and benefits									180,452	139,187	129,886
Noninterest expense	$ 99,939	$ 98,579	$ 115,970	$ 66,631	$ 66,216	$ 65,336	$ 63,936	$ 63,577	381,119	259,065	249,905
Net income before income taxes									72,601	217,753	165,580
Income tax expense	$ 22,800	$ 23,949	$ (40,324)	$ 5,825	$ 13,109	$ 15,492	$ 14,168	$ 15,266	12,250	58,035	42,240
Net income allocated to common stockholders									59,553	158,068	123,340
Corporation
Income
Dividend income from the Bank									29,874	54,118	0
Interest income									22	51	57
Total income									29,896	54,169	57
Expense
Subordinated debentures									16,596	10,680	6,716
Compensation and benefits									3,205	3,106	2,757
Noninterest expense									4,929	2,818	3,384
Total expense									24,730	16,604	12,857
Net income before income taxes									5,166	37,565	(12,800)
Income tax expense									(6,734)	(4,695)	(3,680)
Income (loss) before undistributed income of subsidiary									11,900	42,260	(9,120)
Equity in undistributed earnings of subsidiary									48,451	117,458	132,460
Net income allocated to common stockholders									$ 60,351	$ 159,718	$ 123,340