Cash and Investments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Marketable Securities [Abstract]
Marketable securities	$ 0	$ 245,033,000
Unrealized losses related to marketable securities	(27,000)	(138,000)
Fair value	33,984,000	199,107,000
Available-for-sale securities, continuous unrealized loss position, more than twelve months, fair value	$ 0	$ 0