Parent Company Financial Information - STATEMENTS OF OPERATIONS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Expense
Subordinated debentures									$ 10,680	$ 6,716	$ 4,721
Compensation and benefits									139,187	129,886	84,138
Noninterest expense	$ 66,216	$ 65,336	$ 63,936	$ 63,577	$ 67,239	$ 82,782	$ 50,076	$ 49,808	259,065	249,905	167,958
INCOME BEFORE INCOME TAXES									217,753	165,580	102,226
Income tax	13,109	15,492	14,168	15,266	15,376	7,798	10,182	8,884	58,035	42,240	42,126
Net income	$ 41,098	$ 41,375	$ 38,527	$ 38,718	$ 39,643	$ 28,392	$ 27,303	$ 28,002	158,068	123,340	60,100
Corporation
Income
Dividend income from the Bank									54,118	0	0
Interest income									51	57	36
Total income									54,169	57	36
Expense
Subordinated debentures									10,680	6,716	4,721
Compensation and benefits									3,106	2,757	2,832
Noninterest expense									2,818	3,384	6,123
Total expense									16,604	12,857	13,676
INCOME BEFORE INCOME TAXES									37,565	(12,800)	(13,640)
Income tax									(4,695)	(3,680)	(5,417)
Equity in undistributed earnings of subsidiary									42,260	(9,120)	(8,223)
Equity in undistributed earnings of subsidiary									117,458	132,460	68,323
Net income									$ 159,718	$ 123,340	$ 60,100