Fair Value of Assets and Liabilities - Carrying Amount and Estimated Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Carrying Amount
Financial assets
Cash and cash equivalents	$ 921,207	$ 633,142
Debt securities, held-to-maturity	1,024,730	189,836
Loans receivable, net of ACL	11,086,600	10,964,453
Total financial assets	13,032,537	11,787,431
Financial liabilities
Term deposits	939,563	978,779
Repurchase agreements and other borrowed funds	1,028,757	1,037,651
Subordinated debentures	132,540	139,959
Total financial liabilities	2,100,860	2,156,389
Estimated Fair Value | Level 1
Financial assets
Cash and cash equivalents	921,207	633,142
Debt securities, held-to-maturity	0	0
Loans receivable, net of ACL	0	0
Total financial assets	921,207	633,142
Financial liabilities
Term deposits	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	1,047,013	203,216
Loans receivable, net of ACL	0	0
Total financial assets	1,047,013	203,216
Financial liabilities
Term deposits	942,998	983,491
Repurchase agreements and other borrowed funds	1,028,757	1,037,651
Subordinated debentures	127,765	123,944
Total financial liabilities	2,099,520	2,145,086
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	11,349,564	11,233,002
Total financial assets	11,349,564	11,233,002
Financial liabilities
Term deposits	0	0
Repurchase agreements and other borrowed funds	0	0
Subordinated debentures	0	0
Total financial liabilities	$ 0	$ 0