Capital Stock - Reserved Shares of Common Stock (Detail) - shares	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Issuance in connection with outstanding stock options	997,674	1,570,765	1,949,089	2,244,363
Issuance in connection with restricted stock units outstanding	2,353,315	1,994,790	1,898,025
Reserved for future stock option and restricted stock unit grants	2,572,922	2,464,181
Reserved for future issuance under the employee stock purchase plan	1,298,442	1,161,396
Total	7,222,353	7,191,132