Condensed Parent Company Financial Statements - Statements of Financial Condition (Parent Company Only) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets
Cash and due from banks	$ 196,364	$ 214,894
Total assets	20,838,678	17,850,397
Liabilities and Stockholders' Equity
Subordinated debt	234,768	233,948
Accrued interest payable and other liabilities	355,026	335,620
Stockholders' equity	2,690,006	2,370,793	$ 2,054,998	$ 1,864,874
Total liabilities and stockholders' equity	20,838,678	17,850,397
Parent Company
Assets
Cash and due from banks	442,799	247,507
Investments in and advances to subsidiaries	2,473,520	2,360,467
Other assets	81,192	45,306
Total assets	2,997,511	2,653,280
Liabilities and Stockholders' Equity
Subordinated debt	234,768	233,948
Accrued interest payable and other liabilities	72,737	48,539
Stockholders' equity	2,690,006	2,370,793
Total liabilities and stockholders' equity	$ 2,997,511	$ 2,653,280