Equity - Stock Incentive Plans (Details)	9 Months Ended
	Sep. 30, 2017 USD ($) plan $ / shares shares	Sep. 30, 2016 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based compensation plans (plan) | plan	4
Number of shares [Roll forward]
Outstanding, beginning of period (in shares) | shares	12,552,608
Granted (in shares) | shares	0	0
Exercised (in shares) | shares	(2,417,769)
Unvested options forfeited (in shares) | shares	(25,839)
Vested options expired (in shares) | shares	(68,991)
Outstanding, end of period (in shares) | shares	10,040,009
Vested at end of period (in shares) | shares	9,976,636
Exercisable options, vested and expected to vest (in shares) | shares	10,043,166
Weighted-Average Exercise Price [Roll forward]
Outstanding, weighted average exercise price, beginning of period (in dollars per share)	$ 3.61
Granted, weighted average exercise price (in dollars per share)	0.00
Exercised, weighted average exercise price (in dollars per share)	4.80
Unvested options forfeited, weighted-average exercise price (in dollars per share)	6.54
Vested options expired, weighted-average exercise price (in dollars per share)	5.79
Outstanding, weighted average exercise price, end of period (in dollars per share)	3.30
Vested at end of period, weighted average exercise price (in dollars per share)	3.26
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)	4 years 7 months 6 days
Vested at end of period, weighted average remaining contractual term (in years)	4 years 7 months 2 days
Vested and expected to vest, weighted average remaining contractual term (in years)	4 years 7 months 6 days
Outstanding, aggregate intrinsic value | $	$ 86,178,050
Vested at end of period, aggregate intrinsic value | $	86,042,771
Vested or expected to vest, aggregate intrinsic value | $	86,176,954
Exercised options, intrinsic value | $	$ 17,994,945
Number of outstanding options (in shares) | shares	10,040,009
Outstanding Options, weighted average remaining contractual term (in years)	4 years 7 months 6 days
Outstanding Options, weighted average exercise price (in dollars per share)	$ 3.30
Number of exercisable options (in shares) | shares	9,976,636
Exercisable Options, weighted average exercise price (in dollars per share)	$ 3.26
Total unrecognized compensation expense | $	$ 98,900
$0.70 - $1.09
Stock options, additional disclosures [Abstract]
Outstanding Options, weighted average remaining contractual term (in years)	2 years 9 months 18 days
Exercise Price Range, lower range limit (in dollars per share)	$ 0.70
Exercise Price Range, upper range limit (in dollars per share)	$ 1.09
Number of outstanding options (in shares) | shares	1,094,429
Outstanding Options, weighted average remaining contractual term (in years)	2 years 9 months 18 days
Outstanding Options, weighted average exercise price (in dollars per share)	$ 0.91
Number of exercisable options (in shares) | shares	1,094,429
Exercisable Options, weighted average exercise price (in dollars per share)	$ 0.91
$1.10 - $1.65
Stock options, additional disclosures [Abstract]
Outstanding Options, weighted average remaining contractual term (in years)	3 years 8 months 12 days
Exercise Price Range, lower range limit (in dollars per share)	$ 1.10
Exercise Price Range, upper range limit (in dollars per share)	$ 1.65
Number of outstanding options (in shares) | shares	4,290,379
Outstanding Options, weighted average remaining contractual term (in years)	3 years 8 months 12 days
Outstanding Options, weighted average exercise price (in dollars per share)	$ 1.30
Number of exercisable options (in shares) | shares	4,290,379
Exercisable Options, weighted average exercise price (in dollars per share)	$ 1.30
$2.45 - $3.75
Stock options, additional disclosures [Abstract]
Outstanding Options, weighted average remaining contractual term (in years)	5 years
Exercise Price Range, lower range limit (in dollars per share)	$ 2.45
Exercise Price Range, upper range limit (in dollars per share)	$ 3.75
Number of outstanding options (in shares) | shares	854,001
Outstanding Options, weighted average remaining contractual term (in years)	5 years
Outstanding Options, weighted average exercise price (in dollars per share)	$ 2.77
Number of exercisable options (in shares) | shares	854,001
Exercisable Options, weighted average exercise price (in dollars per share)	$ 2.77
$4.19 - $6.38
Stock options, additional disclosures [Abstract]
Outstanding Options, weighted average remaining contractual term (in years)	5 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	1,989,205
Outstanding Options, weighted average remaining contractual term (in years)	5 years 8 months 12 days
Outstanding Options, weighted average exercise price (in dollars per share)	$ 5.36
Number of exercisable options (in shares) | shares	1,989,205
Exercisable Options, weighted average exercise price (in dollars per share)	$ 5.36
$6.49 - $9.78
Stock options, additional disclosures [Abstract]
Outstanding Options, weighted average remaining contractual term (in years)	6 years 4 months 24 days
Exercise Price Range, lower range limit (in dollars per share)	$ 6.49
Exercise Price Range, upper range limit (in dollars per share)	$ 9.78
Number of outstanding options (in shares) | shares	1,713,328
Outstanding Options, weighted average remaining contractual term (in years)	6 years 4 months 24 days
Outstanding Options, weighted average exercise price (in dollars per share)	$ 7.30
Number of exercisable options (in shares) | shares	1,683,625
Exercisable Options, weighted average exercise price (in dollars per share)	$ 7.26
$9.90 - $10.99
Stock options, additional disclosures [Abstract]
Outstanding Options, weighted average remaining contractual term (in years)	7 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	98,667
Outstanding Options, weighted average remaining contractual term (in years)	7 years 2 months 12 days
Outstanding Options, weighted average exercise price (in dollars per share)	$ 10.38
Number of exercisable options (in shares) | shares	64,997
Exercisable Options, weighted average exercise price (in dollars per share)	$ 10.38