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	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
BASIC:
Net income (loss) attributable to common stockholders – basic	$ 26,639	$ (108,173)	$ (121,510)
Weighted-average common shares outstanding – basic	869,067	878,827	913,511
Net income (loss) per share attributable to common stockholders – basic	$ 0.03	$ (0.12)	$ (0.13)
DILUTED:
Weighted-average common shares outstanding – basic	869,067	878,827	913,511
Weighted-average common shares outstanding-diluted	897,165	878,827	913,511
Net income (loss) per share attributable to common stockholders – diluted	$ 0.03	$ (0.12)	$ (0.13)
Common Class A [Member]
BASIC:
Net income (loss) attributable to common stockholders – basic	$ 23,795	$ (92,988)	$ (103,628)
Weighted-average common shares outstanding – basic	776,625	755,460	779,071
Net income (loss) per share attributable to common stockholders – basic	$ 0.03	$ (0.12)	$ (0.13)
DILUTED:
Net income (loss) attributable to common stockholders-basic	$ 23,795	$ (92,988)	$ (103,628)
Net income (loss) attributable to common stockholders-diluted	$ 26,628	$ (108,173)	$ (121,510)
Weighted-average common shares outstanding – basic	776,625	755,460	779,071
Weighted-average common shares outstanding-diluted	897,165	878,827	913,511
Net income (loss) per share attributable to common stockholders – diluted	$ 0.03	$ (0.12)	$ (0.13)
Common Class A [Member] | Stock options and employee stock purchase plan [Member]
DILUTED:
Weighted-average effect of dilutive securities	9,879
Common Class A [Member] | Restricted Stock Units (ZSUs) [Member]
DILUTED:
Weighted-average effect of dilutive securities	16,935
Common Class A [Member] | Performance Based Restricted Stock Units (ZSUs) [Member]
DILUTED:
Weighted-average effect of dilutive securities	1,284
Common Class B [Member]
BASIC:
Net income (loss) attributable to common stockholders – basic	$ 2,204	$ (12,660)	$ (15,153)
Weighted-average common shares outstanding – basic	71,925	102,850	113,923
Net income (loss) per share attributable to common stockholders – basic	$ 0.03	$ (0.12)	$ (0.13)
DILUTED:
Net income (loss) attributable to common stockholders-basic	$ 2,204	$ (12,660)	$ (15,153)
Net income (loss) attributable to common stockholders-diluted	$ 2,384	$ (12,660)	$ (15,153)
Weighted-average common shares outstanding – basic	71,925	102,850	113,923
Weighted-average common shares outstanding-diluted	80,315	102,850	113,923
Net income (loss) per share attributable to common stockholders – diluted	$ 0.03	$ (0.12)	$ (0.13)
Reallocation of net income (loss) to Class B and Class C shares	$ 180
Common Class B [Member] | Stock options and employee stock purchase plan [Member]
DILUTED:
Weighted-average effect of dilutive securities	8,390
Common Class C [Member]
BASIC:
Net income (loss) attributable to common stockholders – basic	$ 629	$ (2,525)	$ (2,729)
Weighted-average common shares outstanding – basic	20,517	20,517	20,517
Net income (loss) per share attributable to common stockholders – basic	$ 0.03	$ (0.12)	$ (0.13)
DILUTED:
Net income (loss) attributable to common stockholders-basic	$ 629	$ (2,525)	$ (2,729)
Net income (loss) attributable to common stockholders-diluted	$ 609	$ (2,525)	$ (2,729)
Weighted-average common shares outstanding – basic	20,517	20,517	20,517
Weighted-average common shares outstanding-diluted	20,517	20,517	20,517
Net income (loss) per share attributable to common stockholders – diluted	$ 0.03	$ (0.12)	$ (0.13)
Reallocation of net income (loss) to Class B and Class C shares	$ (20)
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	$ 629	$ (2,525)	$ (2,729)
Conversion of common stock class	20,517	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	$ 2,204	$ (12,660)	$ (15,153)
Conversion of common stock class	71,925	102,850	113,923