Basis of Presentation and Accounting Policies - Impact of Adoption to the Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	$ 393,439	$ 311,224	$ 281,343
Inventories	115,025	111,740	111,830
Prepaid expenses and other current assets	122,694	148,469	165,635
Total assets	4,335,386	3,558,639	3,546,014
Accrued expenses	479,120	452,547	443,961
Early access sales accrual	290,457	225,128	232,401
Other liabilities, current portion	59,629	36,456	34,373
Accumulated other comprehensive loss	(4,605)	(10,623)	(11,572)
Accumulated deficit	(4,668,751)	(5,111,443)	(5,119,723)
Total liabilities and shareholders’ equity	4,335,386	3,558,639	$ 3,546,014
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	359,103
Inventories	115,117
Prepaid expenses and other current assets	142,704
Total assets	4,321,152
Accrued expenses	480,892
Early access sales accrual	303,637
Other liabilities, current portion	44,295
Accumulated other comprehensive loss	(4,801)
Accumulated deficit	(4,682,407)
Total liabilities and shareholders’ equity	4,321,152
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	34,336	29,881
Inventories	(92)	(90)
Prepaid expenses and other current assets	(20,010)	(17,166)
Total assets	14,234	12,625
Accrued expenses	(1,772)	8,586
Early access sales accrual	(13,180)	(7,273)
Other liabilities, current portion	15,334	2,083
Accumulated other comprehensive loss	196	949
Accumulated deficit	13,656	8,280
Total liabilities and shareholders’ equity	$ 14,234	$ 12,625