Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property Plant And Equipment [Line Items]
Accumulated depreciation				$ 94,044	$ 94,093
Proceeds from sale of property and equipment				$ 273	$ 3,209	$ 814
Asset Held for Sale [Member] | Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Proceeds from sale of property and equipment	$ 1,300	$ 1,200	$ 400
Asset Held for Sale [Member] | Computer Equipment [Member] | Other Income (Expense), Net [Member]
Property Plant And Equipment [Line Items]
Gain (Loss) on fair value of assets less costs to sell		(300)
Other Current Assets [Member] | Asset Held for Sale [Member] | Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross						83,900
Accumulated depreciation						80,700
Fair value of assets less costs to sell		$ 2,900				$ 3,200