Net Income (Loss) Per Share of Common Stock - Schedule of Computation of Basic and Diluted Net Income (Loss) Per Share of Common Stock (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
BASIC:
Net income (loss) attributable to common stockholders – basic	$ (911)	$ 5,093	$ 4,698	$ (4,381)
Weighted-average common shares outstanding – basic	858,666	863,125	864,117	869,025
Net income (loss) per share attributable to common stockholders – basic	$ 0.00	$ 0.01	$ 0.01	$ (0.01)
DILUTED:
Weighted-average common shares outstanding – basic	858,666	863,125	864,117	869,025
Weighted-average common shares outstanding – diluted	858,666	887,991	890,285	869,025
Net income (loss) per share attributable to common stockholders – diluted	$ 0.00	$ 0.01	$ 0.01	$ (0.01)
Common Class A [Member]
BASIC:
Net income (loss) attributable to common stockholders – basic	$ (911)	$ 4,565	$ 4,698	$ (3,896)
Weighted-average common shares outstanding – basic	858,666	773,704	864,117	772,679
Net income (loss) per share attributable to common stockholders – basic	$ 0.00	$ 0.01	$ 0.01	$ (0.01)
DILUTED:
Net income (loss) attributable to common stockholders – basic	$ (911)	$ 4,565	$ 4,698	$ (3,896)
Net income (loss) attributable to common stockholders – diluted		$ 5,093		$ (4,381)
Weighted-average common shares outstanding – basic	858,666	773,704	864,117	772,679
Weighted-average common shares outstanding – diluted	858,666	887,991	890,285	869,025
Net income (loss) per share attributable to common stockholders – diluted	$ 0.00	$ 0.01	$ 0.01	$ (0.01)
Common Class A [Member] | Stock options and employee stock purchase plan [Member]
DILUTED:
Weighted-average effect of dilutive securities		9,811	10,803
Common Class A [Member] | Restricted Stock Units (ZSUs) [Member]
DILUTED:
Weighted-average effect of dilutive securities		14,710	14,093
Common Class A [Member] | Performance Based Restricted Stock Units (ZSUs) [Member]
DILUTED:
Weighted-average effect of dilutive securities		345	1,272
Common Class B [Member]
BASIC:
Net income (loss) attributable to common stockholders – basic		$ 407		$ (382)
Weighted-average common shares outstanding – basic		68,904		75,289
Net income (loss) per share attributable to common stockholders – basic		$ 0.01		$ (0.01)
DILUTED:
Net income (loss) attributable to common stockholders – basic		$ 407		$ (382)
Net income (loss) attributable to common stockholders – diluted		$ 407		$ (382)
Weighted-average common shares outstanding – basic		68,904		75,289
Weighted-average common shares outstanding – diluted		69,821		75,289
Net income (loss) per share attributable to common stockholders – diluted		$ 0.01		$ (0.01)
Common Class B [Member] | Stock options and employee stock purchase plan [Member]
DILUTED:
Weighted-average effect of dilutive securities		917
Common Class C [Member]
BASIC:
Net income (loss) attributable to common stockholders – basic		$ 121		$ (103)
Weighted-average common shares outstanding – basic		20,517		20,517
Net income (loss) per share attributable to common stockholders – basic		$ 0.01		$ (0.01)
DILUTED:
Net income (loss) attributable to common stockholders – basic		$ 121		$ (103)
Net income (loss) attributable to common stockholders – diluted		$ 121		$ (103)
Weighted-average common shares outstanding – basic		20,517		20,517
Weighted-average common shares outstanding – diluted		20,517		20,517
Net income (loss) per share attributable to common stockholders – diluted		$ 0.01		$ (0.01)
Class C Convert To Class A [Member] | Common Class A [Member]
DILUTED:
Reallocation of net income (loss) as a result of common stock class conversion		$ 121		$ (103)
Conversion of common stock class		20,517		20,517
Class B convert to Class A [Member] | Common Class A [Member]
DILUTED:
Reallocation of net income (loss) as a result of common stock class conversion		$ 407		$ (382)
Conversion of common stock class		68,904		75,829