Parent Company Financial Information - STATEMENTS OF FINANCIAL CONDITION (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Information Disclosure [Abstract]
Percentage of capital stock of the Bank held	100.00%
Assets
Other assets	$ 154,992	$ 89,568
Total assets	11,776,012	11,487,387
Liabilities
Subordinated debentures	215,145	110,313
Accrued expenses and other liabilities	131,367	81,345
Total liabilities	9,763,418	9,517,690
Total Stockholders’ Equity	2,012,594	1,969,697	$ 1,241,996	$ 459,740
Total liabilities and stockholders’ equity	11,776,012	11,487,387
Corporation
Assets
Cash and cash equivalents	13,717	13,160
Investment in subsidiaries	2,217,903	2,068,077
Other assets	1,230	1,689
Total assets	2,232,850	2,082,926
Liabilities
Subordinated debentures	215,145	110,313
Accrued expenses and other liabilities	5,111	2,916
Total liabilities	220,256	113,229
Total Stockholders’ Equity	2,012,594	1,969,697
Total liabilities and stockholders’ equity	$ 2,232,850	$ 2,082,926