Nature of Business and Basis of Presentation - Revision of Prior Period Amounts (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Changes in operating assets and liabilities, net of effects from acquisitions:
Prepaid expenses and other current assets	$ (12,998)	$ (16,208)
Accounts payable and accrued expenses	21,459	23,695
Other non-current assets and liabilities	(8,666)	(1,605)
Net cash provided by operating activities	289,247	234,288
Purchases of property and equipment	(97,992)	(102,222)
Other non-current assets and liabilities	(1,444)	362
Net cash used in investing activities	(864,498)	(159,887)
Proceeds related to the issuance of common stock under stock plans	57,999	28,261
Net cash used in financing activities	493,472	(66,024)
Net increase in cash and cash equivalents	(79,726)	2,876
As previously reported [Member]
Changes in operating assets and liabilities, net of effects from acquisitions:
Prepaid expenses and other current assets		(19,106)
Accounts payable and accrued expenses		25,311
Other non-current assets and liabilities		(1,849)
Net cash provided by operating activities		232,762
Purchases of property and equipment		(100,847)
Other non-current assets and liabilities		0
Net cash used in investing activities		(158,150)
Proceeds related to the issuance of common stock under stock plans		28,050
Net cash used in financing activities		(66,235)
Net increase in cash and cash equivalents		2,876
Adjustment [Member]
Changes in operating assets and liabilities, net of effects from acquisitions:
Prepaid expenses and other current assets		2,898
Accounts payable and accrued expenses		(1,616)
Other non-current assets and liabilities		244
Net cash provided by operating activities		1,526
Purchases of property and equipment		(1,375)
Other non-current assets and liabilities		362
Net cash used in investing activities		(1,737)
Proceeds related to the issuance of common stock under stock plans		211
Net cash used in financing activities		211
Net increase in cash and cash equivalents		$ 0