Fair Value of Assets and Liabilities - Fair Value Measurements on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financial Assets
Debt securities, available-for-sale	$ 5,853,315	$ 5,337,814
Recurring Measurements
Financial Assets
Loans held for sale, at fair value	118,731	166,572
Total assets measured at fair value on a recurring basis	5,983,107	5,513,192
Total financial liabilities		2,056
Interest rate caps \| Recurring Measurements
Financial Assets
Interest rate caps	752	201
Interest rate locks \| Recurring Measurements
Financial Assets
Interest rate caps	6,097	8,605
TBA hedge \| Recurring Measurements
Financial Assets
TBA hedge	4,212	2,056
U.S. government and federal agency \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	35,863	38,588
U.S. government sponsored enterprises \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	5,253	9,781
State and local governments \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	978,652	1,416,683
Corporate bonds \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	288,781	349,098
Residential mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	3,363,627	2,289,090
Commercial mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	1,181,139	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
TBA hedge	0	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	118,731	166,572
Total assets measured at fair value on a recurring basis	5,983,107	5,513,192
Total financial liabilities		2,056
Level 2 \| Interest rate caps \| Recurring Measurements
Financial Assets
Interest rate caps	752	201
Level 2 \| Interest rate locks \| Recurring Measurements
Financial Assets
Interest rate caps	6,097	8,605
Level 2 \| TBA hedge \| Recurring Measurements
Financial Assets
TBA hedge	4,212	2,056
Level 2 \| U.S. government and federal agency \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	35,863	38,588
Level 2 \| U.S. government sponsored enterprises \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	5,253	9,781
Level 2 \| State and local governments \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	978,652	1,416,683
Level 2 \| Corporate bonds \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	288,781	349,098
Level 2 \| Residential mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	3,363,627	2,289,090
Level 2 \| Commercial mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	1,181,139	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
TBA hedge	0	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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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

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