Fair Value of Assets and Liabilities - Carrying Amount and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Carrying Amount
Financial assets
Cash and cash equivalents	$ 633,142	$ 330,961
Debt securities, held-to-maturity	189,836	224,611
Loans receivable, net of ACL	10,964,453	9,388,320
Total financial assets	11,787,431	9,943,892
Financial liabilities
Term deposits	978,779	1,011,798
FHLB advances		38,611
Repurchase agreements and other borrowed funds	1,037,651	598,644
Subordinated debentures	139,959	139,914
Total financial liabilities	2,156,389	1,788,967
Estimated Fair Value | Level 1
Financial assets
Cash and cash equivalents	633,142	330,961
Debt securities, held-to-maturity	0	0
Loans receivable, net of ACL	0	0
Total financial assets	633,142	330,961
Financial liabilities
Term deposits	0	0
FHLB advances		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	203,216	234,396
Loans receivable, net of ACL	0	0
Total financial assets	203,216	234,396
Financial liabilities
Term deposits	983,491	1,017,505
FHLB advances		38,787
Repurchase agreements and other borrowed funds	1,037,651	598,644
Subordinated debentures	123,944	124,094
Total financial liabilities	2,145,086	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	11,233,002	9,438,121
Total financial assets	11,233,002	9,438,121
Financial liabilities
Term deposits	0	0
FHLB advances		0
Repurchase agreements and other borrowed funds	0	0
Subordinated debentures	0	0
Total financial liabilities	$ 0	$ 0