Organization and Summary of Significant Accounting Policies - Additional Information (Detail)				12 Months Ended
		Nov. 01, 2016 USD ($) Reporting_Unit	Nov. 01, 2015 USD ($)	Dec. 31, 2016 USD ($) Practice_Groups Reporting_Unit	Dec. 31, 2015 USD ($) Reporting_Unit	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of practice groups | Practice_Groups				3
Fees earned under administrative service agreement				$ 144,800,000	$ 137,500,000	$ 133,700,000
Maximum maturity period of investments				3 months
Allowance for doubtful accounts				$ 13,508,000	12,659,000	11,915,000	$ 9,975,000
Software purchased or developed, estimated useful life				7 years
Goodwill				$ 487,484,000	447,685,000	435,231,000
Total assets				1,118,588,000	996,331,000
Total stockholders' equity				$ 480,021,000	$ 427,948,000	399,845,000	374,446,000
Number of reporting units | Reporting_Unit		5		5	5
Goodwill, Impairment Loss		$ 0	$ 0
Intangible assets amortization period				7 years 7 months 6 days
Shares vesting term				4 years
Unsecured credit facility				$ 400,000,000
Contract payment terms				90 days
Total personnel costs					$ 544,800,000	502,800,000	$ 487,000,000
Total occupancy costs				$ 45,700,000	41,400,000	$ 37,100,000
Deferred income taxes, net					4,796,000
Net decrease other non-current assets				(2,006,000)	(2,031,000)
Decrease of bank debt	[1]			$ (191,400,000)	(205,800,000)
Restatement Adjustment [Member]
Summary Of Significant Accounting Policies [Line Items]
Net decrease other non-current assets					1,900,000
Decrease of bank debt					1,900,000
Accounting Standards Update 2015-17 [Member]
Summary Of Significant Accounting Policies [Line Items]
Net non-current deferred income tax liability that would have been recorded had a new standard been adopted					$ 100,000
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Intangible assets amortization period				2 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Intangible assets amortization period				15 years

[1] See Note 1, Organization and Summary of Significant Accounting Policies, to the accompanying consolidated financial statements for discussion of our adoption of ASU 2015-03, ASU 2015-15 and ASU 2015-17.