Share Incentive and Other Compensation - Employee 401 (k) Plan - Additional Information (Details)	9 Months Ended
Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Employer matching contribution	50.00%
Maximum annual contribution per employee	6.00%
Maximum employee annual salary contribution	15.00%

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

No definition available.

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration