Condensed Statements of Financial Condition (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets
Cash on hand and in banks	$ 117,137	$ 122,834
Interest bearing cash deposits	70,036	318,550
Cash and cash equivalents	193,253	442,409
Investment securities, available-for-sale	2,610,760	2,387,428
Other assets	71,117	67,828
Total assets	9,089,232	8,306,507
Liabilities and Stockholders' Equity
Subordinated debentures	125,848	125,705
Other liabilities	114,062	102,026
Total liabilities	8,012,582	7,278,460
Common stock	761	750
Paid-in capital	736,368	708,356
Retained earnings	337,532	301,197
Accumulated other comprehensive income	1,989	17,744	$ 9,645	$ 47,962
Total stockholders’ equity	1,076,650	1,028,047	$ 963,250	$ 900,949
Total liabilities and stockholders’ equity	9,089,232	8,306,507
Parent Company
Assets
Cash on hand and in banks	1,854	4,019
Interest bearing cash deposits	46,808	51,127
Cash and cash equivalents	48,662	55,146
Investment securities, available-for-sale	65	91
Other assets	11,553	8,511
Investment in subsidiaries	1,175,844	1,121,937
Total assets	1,236,124	1,185,685
Liabilities and Stockholders' Equity
Dividends Payable	22,893	22,557
Subordinated debentures	125,848	125,705
Other liabilities	10,733	9,376
Total liabilities	159,474	157,638
Common stock	761	750
Paid-in capital	736,368	708,356
Retained earnings	337,532	301,197
Accumulated other comprehensive income	1,989	17,744
Total stockholders’ equity	1,076,650	1,028,047
Total liabilities and stockholders’ equity	$ 1,236,124	$ 1,185,685