Commitments, Credit Risk, and Contingencies - Financial Instrument (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Total commitments subject to credit risk
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instrument whose contract amount represents credit risk	$ 788,012	$ 700,017
Total commitments subject to certain performance criteria and cancellation
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instrument whose contract amount represents credit risk	1,948,100	1,747,409
Commitments to extend credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instrument whose contract amount represents credit risk	761,068	676,987
Standby letters of credit issued by another party on Merchants' behalf
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instrument whose contract amount represents credit risk	26,944	23,030
Outstanding commitments to originate loans
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instrument whose contract amount represents credit risk	886,017	507,216
Unfunded construction draws
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instrument whose contract amount represents credit risk	287,659	457,762
Unfunded lines of warehouse credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instrument whose contract amount represents credit risk	$ 774,424	$ 782,431