Stock-Based Incentive Compensation Plans - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares
Number of Shares
Beginning balance (in shares) | shares	3,001,929
Options granted (in shares) | shares	100,080
Options exercised (in shares) | shares	(395,117)
Options canceled (in shares) | shares	(65,694)
Ending balance (in shares) | shares	2,641,198	3,001,929
Options vested and exercisable (in shares) | shares	1,762,687
Options vested and expected to vest (in shares) | shares	2,366,723
Weighted-Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 4.15
Options granted (in dollars per share) | $ / shares	8.88
Options exercised (in dollars per share) | $ / shares	4.08
Options canceled (in dollars per share) | $ / shares	4.81
Ending balance (in dollars per share) | $ / shares	4.27	$ 4.15
Options vested and exercisable (in dollars per share) | $ / shares	3.73
Options vested and expected to vest (in dollars per share) | $ / shares	$ 4.14
Weighted-Average Remaining Contractual Life and Aggregate Intrinsic Value
Weighted-average remaining contractual life, options outstanding (in years)	6 years 7 months 6 days
Weighted-average remaining contractual life, options vested and exercisable (in years)	5 years 11 months 8 days
Weighted-average remaining contractual life, options vested and expected to vest (in years)	6 years 5 months 27 days
Aggregate intrinsic value | $	$ 43,905	$ 3,585
Aggregate intrinsic value, options vested and exercisable | $	41,882
Aggregate intrinsic value, options vested and expected to vest | $	$ 40,154