Stock-Based Compensation Expense - Additional Information (Detail) - USD ($)			3 Months Ended
	Mar. 15, 2018	Mar. 15, 2017	Mar. 31, 2018	Jan. 30, 2018	Sep. 18, 2017	Mar. 16, 2017	Mar. 16, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Purchase price of common stock by employees (as a percent)			85.00%
Closing price of shares issued (in dollars per share)				$ 22.00
Employee Stock Purchase Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee withholding percentage			15.00%
Restricted Stock And Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense			$ 65,525,000
Unrecognized compensation expense, recognition period			3 years 2 months 12 days
Options to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, recognition period			2 years 3 months 19 days
Unrecognized compensation cost, stock options			$ 10,300,000
Stock options vested, fair value			$ 7,000,000
Stock options granted, weighted-average grant date fair value			$ 11.73
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued to employees (in shares)	123,607	138,085
Aggregate proceeds from issuance of common stock to employees	$ 1,600,000	$ 1,500,000
Share issued, price per share (in dollars per share)		$ 12.79			$ 14.78	$ 12.96	$ 10.60
Closing price of shares issued (in dollars per share)		$ 15.05			$ 17.39	$ 15.25	$ 12.47