Stock-based Awards (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Additional disclosure
Stock-based compensation expense	$ 9,453,000	$ 4,144,000
Options
Number of Options
Outstanding at the beginning of period (in shares)	25,589,876
Granted (in shares)	430,189
Exercised (in shares)	(772,140)
Canceled/forfeited (in shares)	(395,016)
Outstanding at the end of the period (in shares)	24,852,909		25,589,876
Weighted-Average Exercise Price
Outstanding at the beginning of period (in dollars per share)	$ 9.79
Granted (in dollars per share)	$ 17.66
Exercised (in dollars per share)	$ 5.04
Canceled/forfeited (in dollars per share)	$ 12.39
Outstanding at the end of the period (in dollars per share)	$ 10.03		$ 9.79
Weighted Average Remaining Contract Life (in years)
Outstanding at the end of the period	7 years 4 months 21 days		7 years 6 months 18 days
Additional disclosure
Remaining stock-based compensation expense for unvested awards	57,500,000
Weighted average period over which remaining stock based compensation expense for unvested awards is expected to be recognized	2 years 10 months 24 days
Stock-based compensation expense	$ 7,000,000	$ 4,100,000