Stockholders' Deficit - RSU and PSU award activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shares Available For Grant
Shares Available for Grant Beginning Balance (in shares)	1,146,152
Shares Available for Grant Ending Balance (in shares)	769,202	1,146,152
Shares Subject to Outstanding Options, Shares
Outstanding at the beginning of the period (in shares)	1,246,570
Outstanding at the end of the period (in shares)	1,178,660	1,246,570
Shares Subject to Outstanding Options, Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 82.05
Outstanding at the end of the period (in dollars per share)	$ 98.88	$ 82.05
Restricted Stock Units (RSUs)
Shares Available For Grant
Granted (in shares)	(427,668)
Cancelled (in shares)	50,718
Shares Subject to Outstanding Options, Shares
Granted (in shares)	427,668
Cancelled (in shares)	(50,718)
Released (in shares)	(401,484)
Shares Subject to Outstanding Options, Weighted Average Exercise Price
Granted (in dollars per share)	$ 124.87
Cancelled (in dollars per share)	90.21
Released (in dollars per share)	$ 125.83
Performance Stock Units (PSUs)
Shares Subject to Outstanding Options, Shares
Granted (in shares)	0	0	0	55,326
Released (in shares)	(43,376)
Shares Subject to Outstanding Options, Weighted Average Exercise Price
Released (in dollars per share)	$ 122.16