Stockholders' Equity - Net Income Attributable to Noncontrolling Interests (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Change In Ownership Interest [Line Items]
Net Income Attributable to Noncontrolling Interests	$ 1,416	$ 523	$ 3,385	$ 3,400
Noncontrolling interests	57,942		57,942		$ 59,102
Edgewater [Member]
Change In Ownership Interest [Line Items]
Net Income Attributable to Noncontrolling Interests	1,415	520	3,383	3,397
Noncontrolling interests	57,386		57,386		58,568
Other [Member]
Change In Ownership Interest [Line Items]
Net Income Attributable to Noncontrolling Interests	1	$ 3	2	$ 3
Noncontrolling interests	$ 556		$ 556		$ 534