Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Dec. 31, 2018
Debt Instrument Fair Value Disclosure [Abstract]
Transfer of securities between levels of fair value hierarchy	$ 0	$ 0
Days from origination after which mortgage loans are sold			30 days
Amount of non-financial assets (liabilities) measured at fair value on a recurring basis			$ 0	$ 0
Non-financial assets or liabilities for which no impairment was provided			$ 0	$ 0