Fair Value of Assets and Liabilities - Fair Value Measurements on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial Assets
Debt securities, available-for-sale	$ 4,125,548	$ 2,575,252
Recurring Measurements
Financial Assets
Loans held for sale, at fair value	147,937	69,194
Total assets measured at fair value on a recurring basis	4,288,634	2,646,298
Total financial liabilities	1,344	236
Interest rate caps \| Recurring Measurements
Financial Assets
Interest rate caps	182
Interest rate lock commitment \| Recurring Measurements
Financial Assets
Interest rate caps	14,967	1,852
TBA hedge
Financial Assets
TBA hedge
TBA hedge \| Recurring Measurements
Financial Assets
TBA hedge	1,344	236
U.S. government and federal agency \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	40,140	20,044
U.S. government sponsored enterprises \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	9,825	43,677
State and local governments \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	1,275,376	702,398
Corporate bonds \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	361,024	157,602
Residential mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	1,275,858	738,724
Commercial mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	1,163,325	912,807
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	0
Level 1 \| Interest rate caps \| Recurring Measurements
Financial Assets
Interest rate caps	0
Level 1 \| Interest rate lock commitment \| 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	147,937	69,194
Total assets measured at fair value on a recurring basis	4,288,634	2,646,298
Total financial liabilities	1,344	236
Level 2 \| Interest rate caps \| Recurring Measurements
Financial Assets
Interest rate caps	182
Level 2 \| Interest rate lock commitment \| Recurring Measurements
Financial Assets
Interest rate caps	14,967	1,852
Level 2 \| TBA hedge \| Recurring Measurements
Financial Assets
TBA hedge	1,344	236
Level 2 \| U.S. government and federal agency \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	40,140	20,044
Level 2 \| U.S. government sponsored enterprises \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	9,825	43,677
Level 2 \| State and local governments \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	1,275,376	702,398
Level 2 \| Corporate bonds \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	361,024	157,602
Level 2 \| Residential mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	1,275,858	738,724
Level 2 \| Commercial mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	1,163,325	912,807
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	0
Level 3 \| Interest rate caps \| Recurring Measurements
Financial Assets
Interest rate caps	0
Level 3 \| Interest rate lock commitment \| 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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