Fair Value of Assets and Liabilities - Fair Value Measurements on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financial Assets
Debt securities, available-for-sale	$ 7,390,580	$ 5,337,814
Recurring Measurements
Financial Assets
Loans held for sale, at fair value	94,138	166,572
Total assets measured at fair value on a recurring basis	7,489,914	5,513,192
Total financial liabilities		2,056
Interest rate caps \| Recurring Measurements
Financial Assets
Interest rate caps	553	201
Interest rate locks \| Recurring Measurements
Financial Assets
Interest rate caps	3,884	8,605
TBA hedge \| Recurring Measurements
Financial Assets
Interest rate caps	759
TBA hedge		2,056
U.S. government and federal agency \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	31,373	38,588
U.S. government sponsored enterprises \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	47,051	9,781
State and local governments \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	508,691	1,416,683
Corporate bonds \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	198,119	349,098
Residential mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	5,491,345	2,289,090
Commercial mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	1,114,001	1,234,574
Level 1 \| Recurring Measurements
Financial Assets
Loans held for sale, at fair value	0	0
Total assets measured at fair value on a recurring basis	0	0
Total financial liabilities		0
Level 1 \| Interest rate caps \| Recurring Measurements
Financial Assets
Interest rate caps	0	0
Level 1 \| Interest rate locks \| Recurring Measurements
Financial Assets
Interest rate caps	0	0
Level 1 \| TBA hedge \| Recurring Measurements
Financial Assets
Interest rate caps	0
TBA hedge		0
Level 1 \| U.S. government and federal agency \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 1 \| U.S. government sponsored enterprises \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 1 \| State and local governments \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 1 \| Corporate bonds \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 1 \| Residential mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 1 \| Commercial mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 2 \| Recurring Measurements
Financial Assets
Loans held for sale, at fair value	94,138	166,572
Total assets measured at fair value on a recurring basis	7,489,914	5,513,192
Total financial liabilities		2,056
Level 2 \| Interest rate caps \| Recurring Measurements
Financial Assets
Interest rate caps	553	201
Level 2 \| Interest rate locks \| Recurring Measurements
Financial Assets
Interest rate caps	3,884	8,605
Level 2 \| TBA hedge \| Recurring Measurements
Financial Assets
Interest rate caps	759
TBA hedge		2,056
Level 2 \| U.S. government and federal agency \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	31,373	38,588
Level 2 \| U.S. government sponsored enterprises \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	47,051	9,781
Level 2 \| State and local governments \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	508,691	1,416,683
Level 2 \| Corporate bonds \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	198,119	349,098
Level 2 \| Residential mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	5,491,345	2,289,090
Level 2 \| Commercial mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	1,114,001	1,234,574
Level 3 \| Recurring Measurements
Financial Assets
Loans held for sale, at fair value	0	0
Total assets measured at fair value on a recurring basis	0	0
Total financial liabilities		0
Level 3 \| Interest rate caps \| Recurring Measurements
Financial Assets
Interest rate caps	0	0
Level 3 \| Interest rate locks \| Recurring Measurements
Financial Assets
Interest rate caps	0	0
Level 3 \| TBA hedge \| Recurring Measurements
Financial Assets
Interest rate caps	0
TBA hedge		0
Level 3 \| U.S. government and federal agency \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 3 \| U.S. government sponsored enterprises \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 3 \| State and local governments \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 3 \| Corporate bonds \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 3 \| Residential mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 3 \| Commercial mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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