Reserve for Unfunded Commitments - Summary of Activity in Reserve for Unfunded Commitments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Balance at beginning of period	$ 3,864	$ 2,734	$ 3,164	$ 2,719
Provision (reversal of provision) for losses - unfunded commitments	(137)	(135)	563	(120)
Balance at end of period	$ 3,727	$ 2,599	$ 3,727	$ 2,599