Fair Value Measurements - Assets and Liabilities Measured on Non-Recurring Basis (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	$ 0	$ 8,081,000
Real estate owned	0	92,000
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	0	0
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	6,219,008,000	4,841,830,000
Measured on non-recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	1,063,000	125,000
Real estate owned		92,000
Mortgage servicing rights	681,000	442,000
Assets	1,744,000	659,000
Measured on non-recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	0	0
Real estate owned		0
Mortgage servicing rights	0	0
Assets	0	0
Measured on non-recurring basis | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	0	0
Real estate owned		0
Mortgage servicing rights	0	0
Assets	0	0
Measured on non-recurring basis | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	1,063,000	125,000
Real estate owned		92,000
Mortgage servicing rights	681,000	442,000
Assets	$ 1,744,000	$ 659,000