Fair Value Measurements - Additional Information (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) loan	Dec. 31, 2018 USD ($)
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value adjustments | $	$ 0	$ 0
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of residential loans originated for sale in secondary markets	1
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of residential loans originated for sale in secondary markets	4