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Stock-Based Compensation - Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Options (in shares):
Outstanding beginning of the period (in shares)	8,145,777
Granted (in shares)	0
Forfeited (in shares)	(42,110)
Exercised (in shares)	(296,061)
Outstanding end of the period (in shares)	7,807,606		8,145,777
Exercisable at end of the period (in shares)	5,026,156
Weighted-Average Exercise Price (in dollars per share):
Outstanding beginning of the period (in dollars per share)	$ 13.33
Granted (in dollars per share)	0
Forfeited (in dollars per share)	18.30
Exercised (in dollars per share)	10.39
Outstanding end of the period (in dollars per share)	13.42		$ 13.33
Exercisable at the end of the period (in dollars per share)	$ 11.95
Outstanding, weighted-average remaining contractual term (years)	6 years 9 months 18 days		7 years
Exercisable, weighted-average remaining contractual term (years)	5 years 10 months 24 days
Outstanding, aggregate intrinsic value	$ 80,299		$ 65,913
Exercisable, aggregate intrinsic value	59,037
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options exercised intrinsic value	3,600	$ 1,000
Options grants in period, weighted average grant date fair value (in dollars per share)		$ 5.78
Options vested in period fair value	4,600	$ 3,200
Options unrecognized compensation expense	$ 16,700
Employee stock options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options unrecognized compensation expense, period for recognition (years)	2 years 4 months 24 days
Class A Common Stock | Employee stock options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Expiration period (years)	10 years
Minimum | Class A Common Stock | Employee stock options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Award vesting period (years)	3 years
Maximum | Class A Common Stock | Employee stock options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Award vesting period (years)	4 years

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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