Condensed Statements of Financial Condition (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Cash on hand and in banks	$ 161,782	$ 139,948
Interest bearing cash deposits	42,008	60,056
Cash and cash equivalents	203,790	200,004
Other assets	76,651	37,047
Total assets	12,115,484	9,706,349
Liabilities and Stockholders' Equity
Dividends payable	25,726	265	$ 23,137
Subordinated debentures	134,051	126,135
Other liabilities	116,526	73,168
Total liabilities	10,599,630	8,507,292
Common stock	845	780
Paid-in capital	1,051,253	797,997
Retained earnings	473,183	402,259
Accumulated other comprehensive loss	(9,427)	(1,979)
Total stockholders’ equity	1,515,854	1,199,057	$ 1,116,869	$ 1,076,650
Total liabilities and stockholders’ equity	12,115,484	9,706,349
Parent Company
Assets
Cash on hand and in banks	22,000	9,304
Interest bearing cash deposits	42,299	38,420
Cash and cash equivalents	64,299	47,724
Other assets	12,639	8,871
Investment in subsidiaries	1,612,115	1,281,392
Total assets	1,689,053	1,337,987
Liabilities and Stockholders' Equity
Dividends payable	25,726	265
Subordinated debentures	134,051	126,135
Other liabilities	13,422	12,530
Total liabilities	173,199	138,930
Common stock	845	780
Paid-in capital	1,051,253	797,997
Retained earnings	473,183	402,259
Accumulated other comprehensive loss	(9,427)	(1,979)
Total stockholders’ equity	1,515,854	1,199,057
Total liabilities and stockholders’ equity	$ 1,689,053	$ 1,337,987