Equity Compensation (Activity) (Details) - Stock options - $ / shares	3 Months Ended
	Mar. 31, 2016	Jun. 11, 2013
Shares Subject to Options Outstanding
Balance at the beginning of the period (in shares)	4,572,672
Exercised (in shares)	(25,248)
Expired (in shares)	(31,064)
Forfeited (in shares)	(18,496)
Balance at the end of the period (in shares)	4,497,864
Exercisable options (in shares)	3,301,042
Vested and expected to vest at the end of the period (in shares)	4,412,280
Weighted Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 10.72
Exercised (in dollars per share)	4.59
Expired (in dollars per share)	13.20
Forfeited (in dollars per share)	14.97
Balance at the end of the period (in dollars per share)	10.72
Exercisable options at the end of the period (in dollars per share)	9.09
Vested and expected to vest (in dollars per share)	$ 10.64
Weighted-Average Remaining Contractual Life
Exercisable options	5 years 2 months 12 days
Vested and expected to vest	5 years 10 months 24 days
2013 Plan
Stock options
Potential annual increase in shares authorized for issuance as a percentage of shares outstanding as of the preceding December 31		5.00%