Stock Plans - (Summary of Non-vested Stock Option Activity) (Detail) - $ / shares	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Shares, non-vested, beginning balance (in shares)	3,393,441	1,704,230
Shares, granted (in shares)	139,354	394,753
Shares, vested (in shares)	182,069	150,848
Shares, forfeited (in shares)	12,583	20,823
Shares, non-vested, ending balance (in shares)	3,338,143	1,927,312
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted average grant date fair value, non-vested, beginning balance (in dollars per share)	$ 4.56	$ 1.18
Weighted average grant date fair value, granted (in dollars per share)	6.37	3.87
Weighted average grant date fair value, vested (in dollars per share)	1.19	0.58
Weighted average grant date fair value, forfeited (in dollars per share)	3.10	0.95
Weighted average grant date fair value, non-vested, ending balance (in dollars per share)	$ 4.82	$ 1.79