Fair Value of Assets and Liabilities - Carrying Amount and Estimated Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Carrying Amount
Financial assets
Cash and cash equivalents	$ 769,879	$ 330,961
Debt securities, held-to-maturity	193,509	224,611
Loans receivable, net of ACL	11,454,179	9,388,320
Total financial assets	12,417,567	9,943,892
Financial liabilities
Term deposits	1,098,988	1,011,798
FHLB advances	7,318	38,611
Repurchase agreements and other borrowed funds	998,635	598,644
Subordinated debentures	139,918	139,914
Total financial liabilities	2,244,859	1,788,967
Estimated Fair Value | Level 1
Financial assets
Cash and cash equivalents	769,879	330,961
Debt securities, held-to-maturity	0	0
Loans receivable, net of ACL	0	0
Total financial assets	769,879	330,961
Financial liabilities
Term deposits	0	0
FHLB advances	0	0
Repurchase agreements and other borrowed funds	0	0
Subordinated debentures	0	0
Total financial liabilities	0	0
Estimated Fair Value | Level 2
Financial assets
Cash and cash equivalents	0	0
Debt securities, held-to-maturity	206,577	234,396
Loans receivable, net of ACL	0	0
Total financial assets	206,577	234,396
Financial liabilities
Term deposits	1,104,273	1,017,505
FHLB advances	7,537	38,787
Repurchase agreements and other borrowed funds	998,635	598,644
Subordinated debentures	119,318	124,094
Total financial liabilities	2,229,763	1,779,030
Estimated Fair Value | Level 3
Financial assets
Cash and cash equivalents	0	0
Debt securities, held-to-maturity	0	0
Loans receivable, net of ACL	11,619,887	9,438,121
Total financial assets	11,619,887	9,438,121
Financial liabilities
Term deposits	0	0
FHLB advances	0	0
Repurchase agreements and other borrowed funds	0	0
Subordinated debentures	0	0
Total financial liabilities	$ 0	$ 0