Basis of Presentation and Significant Accounting Policies - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2014
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	$ (261,072)	$ (247,047)	$ (500,938)	$ (475,738)
Gross profit	(128,588)	(127,252)	(247,695)	(250,782)
Net loss	$ (3,768)	$ (2,759)	$ (173)	$ (7,546)
Net income per diluted common share (in usd per share)	$ (0.08)	$ (0.06)	$ (0.00)	$ (0.16)
Interest rate of debt, stated percentage	0.75%		0.75%
0.75% Convertible Senior Notes Due 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt discount	$ 63,600		$ 63,600
Interest rate of debt, stated percentage	0.75%		0.75%		0.75%
Effective interest rate percentage	4.98%		4.98%		4.98%
Debt issuance costs | 0.75% Convertible Senior Notes Due 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effective interest rate percentage	5.46%		5.46%		5.46%
Out Of Period Adjustment For Bill And Hold Transactions
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue		$ 4,900		$ 3,400
Gross profit		900		500
Net loss		$ 600		$ 300
Net income per diluted common share (in usd per share)		$ 0.01		$ 0.01