Stockholders' Equity - Net Income Attributable to Noncontrolling Interests (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Change In Ownership Interest [Line Items]
Net Income Attributable to Noncontrolling Interests	$ 1,005	$ 82	$ 1,007	$ 3,900	$ (2,445)	$ 1,269	$ 1,042	$ 6,693	$ 5,994	$ 6,559	$ 6,786
Noncontrolling interests	57,826				53,851				57,826	53,851
LAZ-MD Holdings LLC [Member]
Change In Ownership Interest [Line Items]
Net Income Attributable to Noncontrolling Interests											631
Edgewater [Member]
Change In Ownership Interest [Line Items]
Net Income Attributable to Noncontrolling Interests									5,992	6,557	6,153
Noncontrolling interests	57,238				53,132				57,238	53,132
Other [Member]
Change In Ownership Interest [Line Items]
Net Income Attributable to Noncontrolling Interests									2	2	$ 2
Noncontrolling interests	$ 588				$ 719				$ 588	$ 719