Fair Value of Financial Instruments - Additional Information (Detail) $ / shares in Units, $ in Thousands		3 Months Ended				9 Months Ended
	Dec. 30, 2011 USD ($)	Sep. 30, 2015 USD ($) $ / shares	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($) business	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) $ / shares	Sep. 30, 2014 USD ($)	Jul. 01, 2015 USD ($)	Dec. 31, 2014 USD ($)
Fair Value of Financial Instruments [Abstract]
Investments in notes		$ 34,050				$ 34,050			$ 12,250
Unrealized gain (loss) on investments - debt and equity securities			$ 6,700
Number of businesses acquired | business				1
Contingent consideration remeasurement gain		$ 0		$ 300	$ 150	$ (524)	$ 590
Closing price of common stock | $ / shares		$ 62.53				$ 62.53
1.25% convertible senior notes due 2019
Fair Value of Financial Instruments [Abstract]
Aggregate principal amount		$ 250,000			250,000	$ 250,000	250,000		250,000
Carrying value of equity component		39,287				39,287			$ 39,287
Sky Analytics Inc
Fair Value of Financial Instruments [Abstract]
Contingent consideration related to business acquisitions				$ 900
Convertible debt investment | Shorelight Holdings LLC
Fair Value of Financial Instruments [Abstract]
Investments in notes		27,600			$ 12,500	27,600	$ 12,500
Purchase of additional convertible notes		$ 15,100				$ 15,100		$ 12,000
Debt instrument maturity date						Jul. 01, 2020
Promissory note | Accounting Advisory Practice
Fair Value of Financial Instruments [Abstract]
Promissory note received for sale of Accounting Advisory	$ 3,500
Promissory note term	4 years
Promissory note payable maturity date						Dec. 31, 2018
Discount rate used to measure fair value						17.00%