Nature of Business and Basis of Presentation - Revision of Prior Period Amounts (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Changes in operating assets and liabilities, net of effects from acquisitions:
Prepaid expenses and other current assets	$ (20,961)	$ (11,447)
Accounts payable and accrued expenses	(22,511)	(4,528)
Other non-current assets and liabilities	4,031	(2,295)
Net cash provided by operating activities	89,023	93,224
Purchases of property and equipment	(52,011)	(43,831)
Net cash used in investing activities	(730,458)	(84,239)
Proceeds related to the issuance of common stock under stock plans	44,329	10,364
Net cash used in financing activities	555,508	(43,110)
Net decrease in cash and cash equivalents	(85,165)	(36,714)
As previously reported [Member]
Changes in operating assets and liabilities, net of effects from acquisitions:
Prepaid expenses and other current assets		(14,035)
Accounts payable and accrued expenses		7,838
Other non-current assets and liabilities		(2,257)
Net cash provided by operating activities		103,040
Purchases of property and equipment		(46,478)
Net cash used in investing activities		(86,886)
Proceeds related to the issuance of common stock under stock plans		3,195
Net cash used in financing activities		(50,279)
Net decrease in cash and cash equivalents		(36,714)
Adjustment [Member]
Changes in operating assets and liabilities, net of effects from acquisitions:
Prepaid expenses and other current assets		2,588
Accounts payable and accrued expenses		(12,366)
Other non-current assets and liabilities		(38)
Net cash provided by operating activities		(9,816)
Purchases of property and equipment		2,647
Net cash used in investing activities		2,647
Proceeds related to the issuance of common stock under stock plans		7,169
Net cash used in financing activities		7,169
Net decrease in cash and cash equivalents		$ 0