Stock Based Compensation - Summary of Common Stock Available for Future Grants (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Common Stock Available for Grant
Balance, beginning (in shares)	5,992,621	6,439,532	6,517,310
Grants (in shares)	(2,238,242)	(847,194)	(103,622)
Forfeited/cancelled (in shares)	375,682	397,580	25,641
Shares withheld for tax withholdings (in shares)	203	2,703	203
Balance, ending (in shares)	4,130,264.000	5,992,621	6,439,532