CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Accounts receivable, unbilled services with related parties	$ 1.0	$ 2.3
Pre-funded study costs with related parties	1.0	3.9
Advanced billings with related parties	$ 1.7	$ 7.6
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock shares authorized	5,000,000	5,000,000
Preferred stock shares issued	0	0
Preferred stock shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock shares authorized	250,000,000	250,000,000
Common stock shares issued	35,466,510	40,662,856
Common stock shares outstanding	35,466,510	40,662,856
Treasury stock shares	200,000