Parent Company Financial Information - STATEMENTS OF FINANCIAL CONDITION (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Information Disclosure [Abstract]
Percentage of capital stock of the Bank held	100.00%
Assets
Other assets	$ 292,861	$ 154,992
Total assets	19,736,544	11,776,012
Liabilities
Subordinated debentures	501,511	215,145
Accrued expenses and other liabilities	243,207	131,367
Total liabilities	16,989,895	9,763,418
Total stockholders’ equity	2,746,649	2,012,594	$ 1,969,697	$ 1,241,996
Total liabilities and stockholders’ equity	19,736,544	11,776,012
Corporation
Assets
Cash and cash equivalents	96,827	13,717
Investment in subsidiaries	3,017,285	2,217,903
Other assets	1,301	1,230
Total assets	3,115,413	2,232,850
Liabilities
Subordinated debentures	363,140	215,145
Accrued expenses and other liabilities	5,624	5,111
Total liabilities	368,764	220,256
Total stockholders’ equity	2,746,649	2,012,594
Total liabilities and stockholders’ equity	$ 3,115,413	$ 2,232,850