Stock-Based Compensation - Schedule of Restricted Stock Units by Type (Details) shares in Thousands	12 Months Ended
	Dec. 31, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total restricted stock units vesting conditions granted (in shares)	3,609
Service-based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units vesting conditions granted (in shares)	3,411
Market-based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted with performance based vesting (in shares)	116
Performance-based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted with performance based vesting (in shares)	82