Stock-Based Compensation - Summary of Activity for All Restricted Stock Units ("RSUs") (Details) - Restricted Stock Units (RSUs) shares in Thousands	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Number of awards, unvested, balance (in units) | shares	5,330
Number of awards, granted (in units) | shares	1,778
Number of awards, issued (in units) | shares	(1,206)
Number of awards, forfeited (in units) | shares	(820)
Number of awards, unvested, balance (in units) | shares	5,082
Weighted-average grant date fair value, unvested, beginning balance (in dollars per unit) | $ / shares	$ 5.82
Weighted-average grant date fair value, granted (in dollars per unit) | $ / shares	8.12
Weighted-average grant date fair value, issued (in dollars per unit) | $ / shares	6.57
Weighted-average grant date fair value, forfeited (in dollars per unit) | $ / shares	6.72
Weighted-average grant date fair value, unvested, ending balance (in dollars per unit) | $ / shares	$ 6.49