Condensed Statements of Financial Condition (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets
Cash on hand and in banks	$ 135,268	$ 117,137
Interest bearing cash deposits	17,273	70,036
Cash and cash equivalents	152,541	193,253
Investment securities, available-for-sale	2,425,477	2,610,760
Other assets	74,035	71,117
Total assets	9,450,600	9,089,232
Liabilities and Stockholders' Equity
Dividend payable	23,137	22,893	$ 22,557
Subordinated debentures	125,991	125,848
Other liabilities	102,038	114,062
Total liabilities	8,333,731	8,012,582
Common stock	765	761
Paid-in capital	749,107	736,368
Retained earnings	374,379	337,532
Accumulated other comprehensive (loss) income	(7,382)	1,989	17,744	$ 9,645
Total stockholders’ equity	1,116,869	1,076,650	$ 1,028,047	$ 963,250
Total liabilities and stockholders’ equity	9,450,600	9,089,232
Parent Company
Assets
Cash on hand and in banks	5,906	1,854
Interest bearing cash deposits	57,700	46,808
Cash and cash equivalents	63,606	48,662
Investment securities, available-for-sale	36	65
Other assets	10,764	11,553
Investment in subsidiaries	1,201,667	1,175,844
Total assets	1,276,073	1,236,124
Liabilities and Stockholders' Equity
Dividend payable	23,137	22,893
Subordinated debentures	125,991	125,848
Other liabilities	10,076	10,733
Total liabilities	159,204	159,474
Common stock	765	761
Paid-in capital	749,107	736,368
Retained earnings	374,379	337,532
Accumulated other comprehensive (loss) income	(7,382)	1,989
Total stockholders’ equity	1,116,869	1,076,650
Total liabilities and stockholders’ equity	$ 1,276,073	$ 1,236,124