Stockholders' Equity - Company's Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
2003 Stock Incentive Plan
OUTSTANDING OPTIONS
Outstanding at beginning of period	713,211
Options granted	0	0	0
Options exercised	(46,131)	(16,608)	(28,368)
Outstanding at end of period	667,080	713,211
WEIGHTED-AVERAGE EXERCISE PRICE
Outstanding at beginning of period	$ 1.25
Options exercised	1.29
Outstanding at end of period	$ 1.24	$ 1.25
VESTED AND EXPECTED TO VEST
Outstanding options	667,080
Aggregate Intrinsic Value (in thousands)	$ 5,488
ADDITIONAL DISCLOSURES
Weighted-average exercise price exercisable at end of period	$ 1.24
Weighted-average contractual term (years) exercisable at end of period	1 year 2 months 12 days
Aggregate intrinsic value (in thousands) exercisable at end of period	$ 5,488
Weighted-average contractual term outstanding	1 year 2 months 12 days	2 years 2 months 12 days
Aggregate intrinsic value (in thousands) outstanding at end of period	$ 5,488
2013 Equity Incentive Plan
OUTSTANDING OPTIONS
Outstanding at beginning of period	2,664,163
Options granted	845,479
Options exercised	(144,182)	(54,521)	(3,500)
Options forfeited	(100,206)
Outstanding at end of period	3,265,254	2,664,163
WEIGHTED-AVERAGE EXERCISE PRICE
Outstanding at beginning of period	$ 7.34
Options granted	19.22
Options exercised	6.68
Options forfeited	13.89
Outstanding at end of period	$ 8.39	$ 7.34
VESTED AND EXPECTED TO VEST
Outstanding options	3,265,254
Weighted-Average Exercise Price	$ 8.39
Weighted-Average Remaining Contractual Term	7 years 1 month 6 days
Aggregate Intrinsic Value (in thousands)	$ 7,489
ADDITIONAL DISCLOSURES
Outstanding options exercisable at end of period	2,020,307
Weighted-average exercise price exercisable at end of period	$ 7.66
Weighted-average contractual term (years) exercisable at end of period	6 years 1 month 6 days
Aggregate intrinsic value (in thousands) exercisable at end of period	$ 4,539
Weighted-average contractual term outstanding	7 years 1 month 6 days	7 years 4 months 24 days
Aggregate intrinsic value (in thousands) outstanding at end of period	$ 7,489

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