Compensation and Benefit Plans - Schedule of Employee Stock Ownership Plan (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of ESOP shares purchased | shares	723,751
Shares released to participants (in shares) | shares	48,250
Balance at end of year (in shares) | shares	675,501
New shares purchased (in amount) | $	$ 7,238
Shares released to participants (in amount) | $	483
Balance at end of year (in amount) | $	$ 6,755