Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Class A [Member]	Class A,B, and C Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance, Value at Dec. 31, 2017	$ 1,641,240		$ 5	$ 3,426,500		$ (93,497)	$ (1,691,768)
Beginning balance, Shares at Dec. 31, 2017			870,660,000
Exercise of stock options and ESPP	3,311			3,311
Exercise of stock options and ESPP, Shares			1,510,000
Vesting of ZSUs, net of tax withholdings	(6,364)				$ (6,364)
Vesting of ZSUs, net of tax withholdings, Shares			2,748,000
Stock-based compensation expense	14,113			14,113
Repurchases of common stock, Value	(41,175)				(41,175)
Repurchases of common stock, Shares			(11,306,000)
Retirements of treasury stock					47,539		(47,539)
Adoption of ASU | 2014-09	4,024						4,024
Net income (loss)	5,609						5,609
Other comprehensive income (loss)	23,107					23,107
Ending balance, Value at Mar. 31, 2018	1,643,865		$ 5	3,443,924		(70,390)	(1,729,674)
Ending balance, Shares at Mar. 31, 2018			863,612,000
Beginning balance, Value at Dec. 31, 2017	1,641,240		$ 5	3,426,500		(93,497)	(1,691,768)
Beginning balance, Shares at Dec. 31, 2017			870,660,000
Net income (loss)	4,698	$ 4,698
Other comprehensive income (loss)	(6,614)
Ending balance, Value at Jun. 30, 2018	1,599,594		$ 5	3,462,137		(100,111)	(1,762,437)
Ending balance, Shares at Jun. 30, 2018			860,181,000
Beginning balance, Value at Dec. 31, 2017	1,641,240		$ 5	3,426,500		(93,497)	(1,691,768)
Beginning balance, Shares at Dec. 31, 2017			870,660,000
Ending balance, Value at Dec. 31, 2018	1,596,610	$ 5		3,504,708		(118,439)	(1,789,664)
Ending balance, Shares at Dec. 31, 2018		861,111,000
Beginning balance, Value at Mar. 31, 2018	1,643,865		$ 5	3,443,924		(70,390)	(1,729,674)
Beginning balance, Shares at Mar. 31, 2018			863,612,000
Exercise of stock options and ESPP	844			844
Exercise of stock options and ESPP, Shares			458,000
Vesting of ZSUs, net of tax withholdings	(7,609)				(7,609)
Vesting of ZSUs, net of tax withholdings, Shares			3,013,000
Stock-based compensation expense	17,369			17,369
Repurchases of common stock, Value	(24,243)				(24,243)
Repurchases of common stock, Shares			(6,902,000)
Retirements of treasury stock					31,852		(31,852)
Net income (loss)	(911)	$ (911)					(911)
Other comprehensive income (loss)	(29,721)					(29,721)
Ending balance, Value at Jun. 30, 2018	1,599,594		$ 5	3,462,137		(100,111)	(1,762,437)
Ending balance, Shares at Jun. 30, 2018			860,181,000
Beginning balance, Value at Dec. 31, 2018	1,596,610	$ 5		3,504,708		(118,439)	(1,789,664)
Beginning balance, Shares at Dec. 31, 2018		861,111,000
Exercise of stock options and ESPP	5,304			5,304
Exercise of stock options and ESPP, Shares		5,097,000
Vesting of ZSUs, net of tax withholdings	(11,010)				(11,010)
Vesting of ZSUs, net of tax withholdings, Shares		2,487,000
Acquisition-related common stock issuance	253,903	$ 1		253,902
Acquisition-related common stock issuance, Shares		63,795,000
Stock-based compensation expense	18,773			18,773
Retirements of treasury stock					11,010		(11,010)
Net income (loss)	(128,828)						(128,828)
Other comprehensive income (loss)	6,977					6,977
Ending balance, Value at Mar. 31, 2019	1,741,729	$ 6		3,782,687		(111,462)	(1,929,502)
Ending balance, Shares at Mar. 31, 2019		932,490,000
Beginning balance, Value at Dec. 31, 2018	1,596,610	$ 5		3,504,708		(118,439)	(1,789,664)
Beginning balance, Shares at Dec. 31, 2018		861,111,000
Net income (loss)	(184,658)	$ (184,658)
Other comprehensive income (loss)	(3,587)					(3,587)
Ending balance, Value at Jun. 30, 2019	1,722,951	$ 6		3,846,913		(122,026)	(2,001,942)
Ending balance, Shares at Jun. 30, 2019		940,224,000
Beginning balance, Value at Mar. 31, 2019	1,741,729	$ 6		3,782,687		(111,462)	(1,929,502)
Beginning balance, Shares at Mar. 31, 2019		932,490,000
Exercise of stock options and ESPP	1,727			1,727
Exercise of stock options and ESPP, Shares		3,885,000
Vesting of ZSUs, net of tax withholdings	(16,610)				(16,610)
Vesting of ZSUs, net of tax withholdings, Shares		3,849,000
Stock-based compensation expense	21,355			21,355
Retirements of treasury stock					$ 16,610		(16,610)
Equity component of convertible senior notes	114,974			114,974
Purchase of capped calls related to issuance of convertible seniornotes	(73,830)			(73,830)
Net income (loss)	(55,830)	$ (55,830)					(55,830)
Other comprehensive income (loss)	(10,564)					(10,564)
Ending balance, Value at Jun. 30, 2019	$ 1,722,951	$ 6		$ 3,846,913		$ (122,026)	$ (2,001,942)
Ending balance, Shares at Jun. 30, 2019		940,224,000