Income Taxes - Roll Forward of Liability for Unrecognized Tax Benefits Exclusive of Accrued Interest (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Unrecognized Tax Benefits
Balance, beginning of period	$ 3,396	$ 3,325	$ 3,110
Decrease in previous year tax positions	0	(389)	0
Increase in current year tax positions	448	270	121
Decrease due to lapse of statute of limitations	0	(14)	0
Increase related to adjustment of previous estimates of activity	206	204	94
Balance, end of period	$ 4,050	$ 3,396	$ 3,325