Stockholders' Equity - Net Income Attributable to Noncontrolling Interests (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Change In Ownership Interest [Line Items]
Net Income Attributable to Noncontrolling Interests	$ 1,969	$ 2,877
Noncontrolling interests	59,620		$ 59,102
Edgewater [Member]
Change In Ownership Interest [Line Items]
Net Income Attributable to Noncontrolling Interests	1,968	$ 2,877
Noncontrolling interests	59,062		58,568
Other [Member]
Change In Ownership Interest [Line Items]
Net Income Attributable to Noncontrolling Interests	1
Noncontrolling interests	$ 558		$ 534