Condensed Parent Company Financial Statements - Statements of Financial Condition (Parent Company Only) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Cash and due from banks	$ 211,189	$ 192,800
Other assets	245,734	221,451
Total assets	15,505,649	14,077,052
Liabilities and Stockholders' Equity
Senior and subordinated debt	203,808	195,170
Accrued interest payable and other liabilities	256,652	248,799
Stockholders' equity	2,054,998	1,864,874	$ 1,257,080	$ 1,146,268
Total liabilities and stockholders' equity	15,505,649	14,077,052
Parent Company
Assets
Cash and due from banks	158,026	120,812
Investments in and advances to subsidiaries	2,091,158	1,952,414
Other assets	55,782	43,606
Total assets	2,304,966	2,116,832
Liabilities and Stockholders' Equity
Senior and subordinated debt	203,808	195,170
Accrued interest payable and other liabilities	46,160	56,788
Stockholders' equity	2,054,998	1,864,874
Total liabilities and stockholders' equity	$ 2,304,966	$ 2,116,832