Subsequent Events - Additional Information (Detail) shares in Millions		1 Months Ended	3 Months Ended	9 Months Ended
	Oct. 01, 2015 USD ($) Participants	Oct. 30, 2015 USD ($)	Sep. 30, 2015 USD ($) shares	Sep. 30, 2015 USD ($) shares	Dec. 31, 2014 USD ($)
2010 Notes [Member]
Subsequent Event [Line Items]
Common stock equivalent impact | shares			1.6	1.3
2010 Convertible Senior Subordinated Notes [Member]
Subsequent Event [Line Items]
Principal amount of notes			$ 48,373,000	$ 48,373,000	$ 97,650,000
Common stock equivalent impact | shares			1.6	1.3
Subsequent Event [Member] | Pension Resource Group Inc [Member]
Subsequent Event [Line Items]
Estimated revenue	$ 4,800,000
Consideration paid in cash	$ 2,000,000
Subsequent Event [Member] | Pension Resource Group Inc [Member] | Minimum [Member]
Subsequent Event [Line Items]
Number of clients of acquired entity | Participants	500
Subsequent Event [Member] | Pension Resource Group Inc [Member] | Maximum [Member]
Subsequent Event [Line Items]
Number of clients of acquired entity | Participants	60,000
Subsequent Event [Member] | 2010 Convertible Senior Subordinated Notes [Member]
Subsequent Event [Line Items]
Principal amount of notes	$ 48,400,000
Conversion rate per $ 1,000 principal of convertible notes	$ 1,000
Conversion value of Notes		$ 71,800,000