Organization and Summary of Significant Accounting Policies - Additional Information (Detail) $ / shares in Units, shares in Millions		12 Months Ended
	Aug. 30, 2013 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) Practice_Groups Reporting_Unit	Nov. 01, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Jul. 26, 2013 USD ($)	Dec. 31, 2012 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of practice groups | Practice_Groups		3
Fees earned under administrative service agreement		$ 137,500,000		$ 133,700,000	$ 133,500,000
Maximum maturity period of investments		3 years
Restricted cash		$ 24,860,000		28,293,000
Allowance for doubtful accounts		12,659,000		11,915,000	9,975,000		$ 11,363,000
Funds held for clients		171,497,000		182,847,000
Client fund obligations		$ 171,318,000		183,936,000
Software purchased or developed, estimated useful life		7 years
Property and equipment, net		$ 20,162,000		18,475,000
Goodwill and other intangible assets, net		535,653,000		526,462,000
Total assets		998,200,000		991,244,000
Total stockholders' equity		427,948,000		399,845,000	374,446,000		$ 295,232,000
Goodwill		447,685,000		435,231,000	384,697,000
Goodwill, Impairment Loss		$ 0	$ 0
Number of reporting units | Reporting_Unit		5
Intangible assets amortization period		7 years 9 months 18 days
Shares vesting term		4 years
Contract payment terms		90 days
Total personnel costs		$ 502,800,000		487,000,000	459,800,000
Total occupancy costs		41,400,000		37,100,000	36,000,000
Payment for acquisition of treasury stock		$ 36,482,000		$ 28,137,000	$ 26,468,000
MMP [Member]
Summary Of Significant Accounting Policies [Line Items]
Aggregate Purchase price consideration paid during transaction	$ 201,600,000					$ 201,600,000
Number of shares purchased from Westbury | shares	3.9
Percentage of Holding	50.00%
Common stock, per share amount | $ / shares	$ 6.65
Payment for acquisition of treasury stock	$ 25,700,000
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