401(k) Savings Plan - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($) h	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Compensation And Retirement Disclosure [Abstract]
Age to participate in the savings plan	21 years
Time to participate in the savings plan | h	1,000
Consecutive period to participate in the savings plan	12 months
Discretionary Company contributions | $	$ 0	$ 0	$ 0
Contributions by management	100.00%
Percentage of each participating employee annual cash compensation	3.00%
Employee's contributions	50.00%
Additional annual cash compensation	2.00%