Fair Value Measurements - Assets and liabilities recorded at fair value on recurring basis (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	$ 1,775,633	$ 2,623,408
Assets measured at fair value on a nonrecurring basis	1,811,703
U. S. agency securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	706,553	622,387
Residential mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	1,004,425	1,677,673
Loans held for sale	25,504	47,218
Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	15,179	145,431
Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	1,983	128,459
Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	25,504	47,218
Assets measured at fair value on a nonrecurring basis		2,676,459
Derivative liability	17	47
Total liabilities measured at fair value on a recurring basis	9,928	5,194
Recurring \| Interest rate caps
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	10,357	5,197
Derivative liability	9,911	5,147
Recurring \| U. S. agency securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	706,554	622,387
Recurring \| Residential mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	1,004,425	1,677,673
Recurring \| Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	15,179	145,431
Recurring \| Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	1,983	128,459
Recurring \| Mortgage banking derivatives \| Derivative Financial Instruments, Assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	209	636
Recurring \| U.S. treasury bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	47,492	49,458
Recurring \| Fair Value, Inputs, Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	0	0
Assets measured at fair value on a nonrecurring basis	0	0
Derivative liability	0	0
Total liabilities measured at fair value on a recurring basis	0	0
Recurring \| Fair Value, Inputs, Level 1 \| Interest rate caps
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	0	0
Derivative liability	0	0
Recurring \| Fair Value, Inputs, Level 1 \| U. S. agency securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	0	0
Recurring \| Fair Value, Inputs, Level 1 \| Residential mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	0	0
Recurring \| Fair Value, Inputs, Level 1 \| Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	0	0
Recurring \| Fair Value, Inputs, Level 1 \| Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	0	0
Recurring \| Fair Value, Inputs, Level 1 \| Mortgage banking derivatives \| Derivative Financial Instruments, Assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	0	0
Recurring \| Fair Value, Inputs, Level 1 \| U.S. treasury bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	0	0
Recurring \| Fair Value, Inputs, Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	25,504	47,218
Assets measured at fair value on a nonrecurring basis	1,811,494	2,663,823
Derivative liability	17	47
Total liabilities measured at fair value on a recurring basis	9,928	5,194
Recurring \| Fair Value, Inputs, Level 2 \| Interest rate caps
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	10,357	5,197
Derivative liability	9,911	5,147
Recurring \| Fair Value, Inputs, Level 2 \| U. S. agency securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	706,554	622,387
Recurring \| Fair Value, Inputs, Level 2 \| Residential mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	1,004,425	1,677,673
Recurring \| Fair Value, Inputs, Level 2 \| Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	15,179	145,431
Recurring \| Fair Value, Inputs, Level 2 \| Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	1,983	116,459
Recurring \| Fair Value, Inputs, Level 2 \| Mortgage banking derivatives \| Derivative Financial Instruments, Assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	0	0
Recurring \| Fair Value, Inputs, Level 2 \| U.S. treasury bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	47,492	49,458
Recurring \| Fair Value, Inputs, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	0	0
Assets measured at fair value on a nonrecurring basis	209	12,636
Derivative liability	0	0
Total liabilities measured at fair value on a recurring basis	0	0
Recurring \| Fair Value, Inputs, Level 3 \| Interest rate caps
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	0	0
Derivative liability	0	0
Recurring \| Fair Value, Inputs, Level 3 \| U. S. agency securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	0	0
Recurring \| Fair Value, Inputs, Level 3 \| Residential mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	0	0
Recurring \| Fair Value, Inputs, Level 3 \| Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	0	0
Recurring \| Fair Value, Inputs, Level 3 \| Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available-for-sale:	0	12,000
Recurring \| Fair Value, Inputs, Level 3 \| Mortgage banking derivatives \| Derivative Financial Instruments, Assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	209	636
Recurring \| Fair Value, Inputs, Level 3 \| U.S. treasury bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment 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, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value of financial and nonfinancial obligations.

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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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