Equity - Stock Incentive Plans (Details)	9 Months Ended
	Sep. 30, 2016 USD ($) plan $ / shares shares	Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based compensation plans | plan	4
Number of shares [Roll forward]
Outstanding, beginning of period (in shares) | shares	14,019,629
Granted (in shares) | shares	0
Exercised (in shares) | shares	(926,010)
Unvested options forfeited (in shares) | shares	(93,097)
Vested options expired (in shares) | shares	(38,354)
Outstanding, end of period (in shares) | shares	12,962,168
Vested at end of period (in shares) | shares	11,818,559
Exercisable options, vested and expected to vest (in shares) | shares	12,937,248
Weighted-Average Exercise Price [Roll forward]
Outstanding, weighted average exercise price, beginning of period (in dollars per share)	$ 3.62
Granted, weighted average exercise price (in dollars per share)	0.00
Exercised, weighted average exercise price (in dollars per share)	2.76
Unvested options forfeited, weighted-average exercise price (in dollars per share)	6.52
Vested options expired, weighted-average exercise price (in dollars per share)	6.77
Outstanding, weighted average exercise price, end of period (in dollars per share)	3.65
Vested at end of period, weighted average exercise price (in dollars per share)	3.30
Vested and expected to vest, weighted average exercise price (in dollars per share)	$ 3.30
Stock options, additional disclosures [Abstract]
Outstanding Options, weighted average remaining contractual term (in years)	5 years 9 months 7 days
Vested at end of period, weighted average remaining contractual term (in years)	5 years 7 months 13 days
Vested and expected to vest, weighted average remaining contractual term (in years)	5 years 7 months 13 days
Outstanding, aggregate intrinsic value | $	$ 64,153,271
Vested at end of period, aggregate intrinsic value | $	62,449,678
Vested or expected to vest, aggregate intrinsic value | $	64,120,370
Exercised options, intrinsic value | $	$ 5,283,449
Number of outstanding options (in shares) | shares	12,962,168
Outstanding Options, weighted average remaining contractual term (in years)	5 years 9 months 7 days
Outstanding Options, weighted average exercise price (in dollars per share)	$ 3.65
Number of exercisable options (in shares) | shares	11,818,559
Exercisable Options, weighted average exercise price (in dollars per share)	$ 3.30
Total unrecognized compensation expense | $	$ 2,150,652
Fair value options valuation assumptions [Abstract]
Expected volatility Minimum		54.40%
Expected volatility Maximum		58.10%
Expected life (in years)		6 years
Expected dividend yield		0.00%
Risk-free interest rate Minimum		1.51%
Risk-free interest rate Maximum		1.68%
$0.50 - $0.76
Stock options, additional disclosures [Abstract]
Outstanding Options, weighted average remaining contractual term (in years)	2 years 7 months 6 days
Exercise Price Range, lower range limit (in dollars per share)	$ 0.50
Exercise Price Range, upper range limit (in dollars per share)	$ 0.76
Number of outstanding options (in shares) | shares	441,429
Outstanding Options, weighted average remaining contractual term (in years)	2 years 7 months 6 days
Outstanding Options, weighted average exercise price (in dollars per share)	$ 0.72
Number of exercisable options (in shares) | shares	441,429
Exercisable Options, weighted average exercise price (in dollars per share)	$ 0.72
$0.87 - $1.35
Stock options, additional disclosures [Abstract]
Outstanding Options, weighted average remaining contractual term (in years)	4 years 10 months 24 days
Exercise Price Range, lower range limit (in dollars per share)	$ 0.87
Exercise Price Range, upper range limit (in dollars per share)	$ 1.35
Number of outstanding options (in shares) | shares	4,397,970
Outstanding Options, weighted average remaining contractual term (in years)	4 years 10 months 24 days
Outstanding Options, weighted average exercise price (in dollars per share)	$ 1.19
Number of exercisable options (in shares) | shares	4,397,970
Exercisable Options, weighted average exercise price (in dollars per share)	$ 1.19
$1.40 - $2.45
Stock options, additional disclosures [Abstract]
Outstanding Options, weighted average remaining contractual term (in years)	4 years 2 months 12 days
Exercise Price Range, lower range limit (in dollars per share)	$ 1.40
Exercise Price Range, upper range limit (in dollars per share)	$ 2.45
Number of outstanding options (in shares) | shares	1,442,424
Outstanding Options, weighted average remaining contractual term (in years)	4 years 2 months 12 days
Outstanding Options, weighted average exercise price (in dollars per share)	$ 1.92
Number of exercisable options (in shares) | shares	1,442,424
Exercisable Options, weighted average exercise price (in dollars per share)	$ 1.92
$2.66 - $3.99
Stock options, additional disclosures [Abstract]
Outstanding Options, weighted average remaining contractual term (in years)	6 years 1 month 6 days
Exercise Price Range, lower range limit (in dollars per share)	$ 2.66
Exercise Price Range, upper range limit (in dollars per share)	$ 3.99
Number of outstanding options (in shares) | shares	889,430
Outstanding Options, weighted average remaining contractual term (in years)	6 years 1 month 6 days
Outstanding Options, weighted average exercise price (in dollars per share)	$ 3.06
Number of exercisable options (in shares) | shares	889,430
Exercisable Options, weighted average exercise price (in dollars per share)	$ 3.06
$4.19 - $6.38
Stock options, additional disclosures [Abstract]
Outstanding Options, weighted average remaining contractual term (in years)	6 years 8 months 12 days
Exercise Price Range, lower range limit (in dollars per share)	$ 4.19
Exercise Price Range, upper range limit (in dollars per share)	$ 6.38
Number of outstanding options (in shares) | shares	3,253,783
Outstanding Options, weighted average remaining contractual term (in years)	6 years 8 months 12 days
Outstanding Options, weighted average exercise price (in dollars per share)	$ 5.36
Number of exercisable options (in shares) | shares	2,997,303
Exercisable Options, weighted average exercise price (in dollars per share)	$ 5.32
$6.45 - $9.78
Stock options, additional disclosures [Abstract]
Outstanding Options, weighted average remaining contractual term (in years)	7 years 4 months 24 days
Exercise Price Range, lower range limit (in dollars per share)	$ 6.45
Exercise Price Range, upper range limit (in dollars per share)	$ 9.78
Number of outstanding options (in shares) | shares	2,431,132
Outstanding Options, weighted average remaining contractual term (in years)	7 years 4 months 24 days
Outstanding Options, weighted average exercise price (in dollars per share)	$ 7.30
Number of exercisable options (in shares) | shares	1,614,677
Exercisable Options, weighted average exercise price (in dollars per share)	$ 7.23
$9.90- $10.99
Stock options, additional disclosures [Abstract]
Outstanding Options, weighted average remaining contractual term (in years)	8 years 2 months 12 days
Exercise Price Range, lower range limit (in dollars per share)	$ 9.90
Exercise Price Range, upper range limit (in dollars per share)	$ 10.99
Number of outstanding options (in shares) | shares	106,000
Outstanding Options, weighted average remaining contractual term (in years)	8 years 2 months 12 days
Outstanding Options, weighted average exercise price (in dollars per share)	$ 10.43
Number of exercisable options (in shares) | shares	35,326
Exercisable Options, weighted average exercise price (in dollars per share)	$ 10.43