Fair Value of Assets and Liabilities - Carrying Amount and Estimated Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Carrying Amount
Financial assets
Cash and cash equivalents	$ 878,450	$ 633,142
Debt securities, held-to-maturity	588,751	189,836
Loans receivable, net of ACL	11,113,483	10,964,453
Total financial assets	12,580,684	11,787,431
Financial liabilities
Term deposits	965,986	978,779
Repurchase agreements and other borrowed funds	1,030,330	1,037,651
Subordinated debentures	132,499	139,959
Total financial liabilities	2,128,815	2,156,389
Estimated Fair Value | Level 1
Financial assets
Cash and cash equivalents	878,450	633,142
Debt securities, held-to-maturity	0	0
Loans receivable, net of ACL	0	0
Total financial assets	878,450	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	598,960	203,216
Loans receivable, net of ACL	0	0
Total financial assets	598,960	203,216
Financial liabilities
Term deposits	970,127	983,491
Repurchase agreements and other borrowed funds	1,030,330	1,037,651
Subordinated debentures	126,452	123,944
Total financial liabilities	2,126,909	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	11,388,533	11,233,002
Total financial assets	11,388,533	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