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, 2021	Dec. 31, 2020
Carrying Amount
Financial assets
Cash and cash equivalents	$ 348,888	$ 633,142
Debt securities, held-to-maturity	1,128,299	189,836
Loans receivable, net of ACL	11,140,282	10,964,453
Total financial assets	12,617,469	11,787,431
Financial liabilities
Term deposits	919,852	978,779
Repurchase agreements and other borrowed funds	1,074,610	1,037,651
Subordinated debentures	132,580	139,959
Total financial liabilities	2,127,042	2,156,389
Estimated Fair Value | Level 1
Financial assets
Cash and cash equivalents	348,888	633,142
Debt securities, held-to-maturity	0	0
Loans receivable, net of ACL	0	0
Total financial assets	348,888	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	1,146,453	203,216
Loans receivable, net of ACL	0	0
Total financial assets	1,146,453	203,216
Financial liabilities
Term deposits	922,810	983,491
Repurchase agreements and other borrowed funds	1,074,610	1,037,651
Subordinated debentures	130,081	123,944
Total financial liabilities	2,127,501	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	11,352,711	11,233,002
Total financial assets	11,352,711	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