Consolidated Statements of Stockholders' Equity - 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	$ 5,047					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
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
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)					(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