Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash equivalents maturity period		3 months
Short-term investments maturity period		90 days
Period of royalties notification, minimum		30 days
Period of royalties notification, maximum		45 days
Advertising expense		$ 221	$ 102	$ 265
Period of maturities, money market and highly liquid debt		90 days
Pro Forma | Accounting Standards Update 2014-09
Item Effected [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax	$ (5,200)