Stockholders' Deficit - Stock options outstanding (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Options Outstanding
Number Outstanding (in shares) | shares	11,206,553
Options Exercisable
Number Exercisable (in shares) | shares	7,250,283
Range of Exercise Prices $2.80 - $17.79
Stock options outstanding
Exercise price, lower range limit (in dollars per share)	$ 2.80
Exercise price, upper range limit (in dollars per share)	$ 17.79
Options Outstanding
Number Outstanding (in shares) | shares	1,460,251
Weighted Average Remaining Contractual Life	11 months 9 days
Weighted Average Exercise Price (in dollars per share)	$ 16.13
Options Exercisable
Number Exercisable (in shares) | shares	1,460,251
Weighted Average Exercise Price (in dollars per share)	$ 16.13
Range of Exercise Prices $17.89 - $18.30
Stock options outstanding
Exercise price, lower range limit (in dollars per share)	17.89
Exercise price, upper range limit (in dollars per share)	$ 18.30
Options Outstanding
Number Outstanding (in shares) | shares	105,542
Weighted Average Remaining Contractual Life	1 year 6 months
Weighted Average Exercise Price (in dollars per share)	$ 18.12
Options Exercisable
Number Exercisable (in shares) | shares	105,542
Weighted Average Exercise Price (in dollars per share)	$ 18.12
Range of Exercise Prices $18.32 - $18.32
Stock options outstanding
Exercise price, lower range limit (in dollars per share)	18.32
Exercise price, upper range limit (in dollars per share)	$ 18.32
Options Outstanding
Number Outstanding (in shares) | shares	1,634,218
Weighted Average Remaining Contractual Life	2 years 1 month 2 days
Weighted Average Exercise Price (in dollars per share)	$ 18.32
Options Exercisable
Number Exercisable (in shares) | shares	1,634,218
Weighted Average Exercise Price (in dollars per share)	$ 18.32
Range of Exercise Prices $18.97 - $64.55
Stock options outstanding
Exercise price, lower range limit (in dollars per share)	18.97
Exercise price, upper range limit (in dollars per share)	$ 64.55
Options Outstanding
Number Outstanding (in shares) | shares	1,605,405
Weighted Average Remaining Contractual Life	3 years 1 month 28 days
Weighted Average Exercise Price (in dollars per share)	$ 47.54
Options Exercisable
Number Exercisable (in shares) | shares	1,605,405
Weighted Average Exercise Price (in dollars per share)	$ 47.54
Range of Exercise Prices $67.06 - $73.21
Stock options outstanding
Exercise price, lower range limit (in dollars per share)	67.06
Exercise price, upper range limit (in dollars per share)	$ 73.21
Options Outstanding
Number Outstanding (in shares) | shares	1,168,504
Weighted Average Remaining Contractual Life	4 years 9 months 18 days
Weighted Average Exercise Price (in dollars per share)	$ 73.09
Options Exercisable
Number Exercisable (in shares) | shares	828,825
Weighted Average Exercise Price (in dollars per share)	$ 73.06
Range of Exercise Prices $73.29 - $85.49
Stock options outstanding
Exercise price, lower range limit (in dollars per share)	73.29
Exercise price, upper range limit (in dollars per share)	$ 85.49
Options Outstanding
Number Outstanding (in shares) | shares	1,137,905
Weighted Average Remaining Contractual Life	8 years 7 days
Weighted Average Exercise Price (in dollars per share)	$ 82.88
Options Exercisable
Number Exercisable (in shares) | shares	508,487
Weighted Average Exercise Price (in dollars per share)	$ 82.45
Range of Exercise Prices $88.46 - $95.54
Stock options outstanding
Exercise price, lower range limit (in dollars per share)	88.46
Exercise price, upper range limit (in dollars per share)	$ 95.54
Options Outstanding
Number Outstanding (in shares) | shares	198,735
Weighted Average Remaining Contractual Life	7 years 8 months 19 days
Weighted Average Exercise Price (in dollars per share)	$ 91.49
Options Exercisable
Number Exercisable (in shares) | shares	81,033
Weighted Average Exercise Price (in dollars per share)	$ 90.38
Range of Exercise Prices $95.76 - $95.76
Stock options outstanding
Exercise price, lower range limit (in dollars per share)	95.76
Exercise price, upper range limit (in dollars per share)	$ 95.76
Options Outstanding
Number Outstanding (in shares) | shares	1,161,545
Weighted Average Remaining Contractual Life	5 years 9 months
Weighted Average Exercise Price (in dollars per share)	$ 95.76
Options Exercisable
Number Exercisable (in shares) | shares	539,083
Weighted Average Exercise Price (in dollars per share)	$ 95.76
Range of Exercise Prices $101.00 - $109.68
Stock options outstanding
Exercise price, lower range limit (in dollars per share)	101.00
Exercise price, upper range limit (in dollars per share)	$ 109.68
Options Outstanding
Number Outstanding (in shares) | shares	262,613
Weighted Average Remaining Contractual Life	7 years 5 months 1 day
Weighted Average Exercise Price (in dollars per share)	$ 106.54
Options Exercisable
Number Exercisable (in shares) | shares	154,362
Weighted Average Exercise Price (in dollars per share)	$ 107.32
Range of Exercise Prices $113.64 - $138.52
Stock options outstanding
Exercise price, lower range limit (in dollars per share)	113.64
Exercise price, upper range limit (in dollars per share)	$ 138.52
Options Outstanding
Number Outstanding (in shares) | shares	2,471,835
Weighted Average Remaining Contractual Life	9 years 1 month 17 days
Weighted Average Exercise Price (in dollars per share)	$ 120.26
Options Exercisable
Number Exercisable (in shares) | shares	333,077
Weighted Average Exercise Price (in dollars per share)	$ 115.11