Stock-based Compensation - Company's Options Outstanding (Detail)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding - Number of Shares (in shares)	5,042,352
Options Exercisable - Number of Shares (in shares)	3,381,664
$1.92
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price, Minimum (in dollars per share) | $ / shares	$ 0
Exercise Price, Maximum (in dollars per share) | $ / shares	$ 1.92
Options Outstanding - Number of Shares (in shares)	357,609
Options Outstanding -Weighted- Average Remaining Contractual Life in Years	3 years 2 months 20 days
Options Exercisable - Number of Shares (in shares)	357,609
Options Exercisable - Weighted- Average Remaining Contractual Life in Years	3 years 2 months 20 days
$2.24 – $6.72
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price, Minimum (in dollars per share) | $ / shares	$ 2.24
Exercise Price, Maximum (in dollars per share) | $ / shares	$ 6.72
Options Outstanding - Number of Shares (in shares)	344,531
Options Outstanding -Weighted- Average Remaining Contractual Life in Years	2 years 7 months 13 days
Options Exercisable - Number of Shares (in shares)	336,231
Options Exercisable - Weighted- Average Remaining Contractual Life in Years	2 years 5 months 15 days
$6.80 – $12.56
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price, Minimum (in dollars per share) | $ / shares	$ 6.80
Exercise Price, Maximum (in dollars per share) | $ / shares	$ 12.56
Options Outstanding - Number of Shares (in shares)	1,225,090
Options Outstanding -Weighted- Average Remaining Contractual Life in Years	7 years 11 months 10 days
Options Exercisable - Number of Shares (in shares)	462,948
Options Exercisable - Weighted- Average Remaining Contractual Life in Years	6 years 1 month 26 days
$12.77
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price, Minimum (in dollars per share) | $ / shares	$ 12.77
Exercise Price, Maximum (in dollars per share) | $ / shares	$ 12.77
Options Outstanding - Number of Shares (in shares)	484,976
Options Outstanding -Weighted- Average Remaining Contractual Life in Years	5 years 9 months 30 days
Options Exercisable - Number of Shares (in shares)	463,659
Options Exercisable - Weighted- Average Remaining Contractual Life in Years	5 years 9 months 26 days
$12.89 – $12.94
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price, Minimum (in dollars per share) | $ / shares	$ 12.89
Exercise Price, Maximum (in dollars per share) | $ / shares	$ 12.94
Options Outstanding - Number of Shares (in shares)	436,867
Options Outstanding -Weighted- Average Remaining Contractual Life in Years	6 years 10 months 24 days
Options Exercisable - Number of Shares (in shares)	298,921
Options Exercisable - Weighted- Average Remaining Contractual Life in Years	6 years 8 months 22 days
$13.01 – $14.95
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price, Minimum (in dollars per share) | $ / shares	$ 13.01
Exercise Price, Maximum (in dollars per share) | $ / shares	$ 14.95
Options Outstanding - Number of Shares (in shares)	322,713
Options Outstanding -Weighted- Average Remaining Contractual Life in Years	7 years 2 months 21 days
Options Exercisable - Number of Shares (in shares)	223,186
Options Exercisable - Weighted- Average Remaining Contractual Life in Years	6 years 7 months 10 days
$14.99 – $17.48
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price, Minimum (in dollars per share) | $ / shares	$ 14.99
Exercise Price, Maximum (in dollars per share) | $ / shares	$ 17.48
Options Outstanding - Number of Shares (in shares)	464,533
Options Outstanding -Weighted- Average Remaining Contractual Life in Years	7 years 4 months 6 days
Options Exercisable - Number of Shares (in shares)	293,914
Options Exercisable - Weighted- Average Remaining Contractual Life in Years	6 years 9 months 10 days
$17.83 – $18.90
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price, Minimum (in dollars per share) | $ / shares	$ 17.83
Exercise Price, Maximum (in dollars per share) | $ / shares	$ 18.90
Options Outstanding - Number of Shares (in shares)	1,150,432
Options Outstanding -Weighted- Average Remaining Contractual Life in Years	6 years 5 months 27 days
Options Exercisable - Number of Shares (in shares)	777,347
Options Exercisable - Weighted- Average Remaining Contractual Life in Years	5 years 7 months 13 days
$19.09 – $22.71
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price, Minimum (in dollars per share) | $ / shares	$ 19.09
Exercise Price, Maximum (in dollars per share) | $ / shares	$ 22.71
Options Outstanding - Number of Shares (in shares)	255,601
Options Outstanding -Weighted- Average Remaining Contractual Life in Years	7 years 3 months 5 days
Options Exercisable - Number of Shares (in shares)	167,849
Options Exercisable - Weighted- Average Remaining Contractual Life in Years	7 years 1 month 14 days