Fair Value Measurements - Financial assets measured at fair value on a recurring basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Cash, including short-term deposits [Member]
Financial Assets	$ 120,214	[1]	$ 68,265	[1]
Cash, including short-term deposits [Member] | Cash And Cash Equivalent [Member]
Financial Assets			68,200
Cash, including short-term deposits [Member] | Marketable Securities [Member]
Financial Assets			100
Cash, including short-term deposits [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets	120,214	[1]	68,265	[1]
Cash, including short-term deposits [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets	0	[1]	0	[1]
Cash, including short-term deposits [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets	0	[1]	0	[1]
Mutual Funds [Member]
Financial Assets	16,129	[2]	11,820	[2]
Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets	16,129	[2]	11,820	[2]
Mutual Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets	0	[2]	0	[2]
Mutual Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets	0	[2]	0	[2]
US Treasury and Government [Member]
Financial Assets	50,412	[2]	99,477	[2]
US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets	50,412	[2]	99,477	[2]
US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets	0	[2]	0	[2]
US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets	0	[2]	0	[2]
Corporate Securities [Member]
Financial Assets	73,970	[2]	20,117	[2]
Corporate Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets	67,922	[2]	20,117	[2]
Corporate Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets	0	[2]	0	[2]
Corporate Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets	6,048	[2]	0	[2]
Commercial Paper [Member]
Financial Assets	6,298	[3]	22,291	[4]
Commercial Paper [Member] | Cash And Cash Equivalent [Member]
Financial Assets	1,700		3,400	[2]
Commercial Paper [Member] | Marketable Securities [Member]
Financial Assets	4,600		18,900	[2]
Commercial Paper [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets	0	[3]	0	[4]
Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets	6,298	[3]	22,291	[4]
Commercial Paper [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets	0	[3]	0	[4]
Corporate Obligations [Member]
Financial Assets	24,386	[2]	48,714	[2]
Corporate Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets	0	[2]	0	[2]
Corporate Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets	12,573	[2]	46,931	[2]
Corporate Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets	11,813	[2]	1,783	[2]
Non-controlling interests in certain funds [Member]
Financial Assets	849	[5]	1,021	[6]
Non-controlling interests in certain funds [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets	0	[5]	0	[6]
Non-controlling interests in certain funds [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets	0	[5]	0	[6]
Non-controlling interests in certain funds [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets	849	[5]	1,021	[6]
Financial Assets [Member]
Financial Assets	292,258		271,705
Financial Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets	254,677		199,679
Financial Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets	18,871		69,222
Financial Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets	18,710		2,804
Acquisition-related contingent consideration [Member]
Financial Liabilities			(475)	[7]
Acquisition-related contingent consideration [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Liabilities			0	[7]
Acquisition-related contingent consideration [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Liabilities			0	[7]
Acquisition-related contingent consideration [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Liabilities			$ (475)

[1] Reported within "Cash and cash equivalents".

[2] Reported within “Marketable securities”

[3] At September 30, 2013, the Company reported $1.7 million and $4.6 million within "Cash and cash equivalents" and "Marketable securities", respectively.

[4] At December 31, 2012, the Company reported $3.4 million and $18.9 million within "Cash and cash equivalents" and "Marketable securities."

[5] Reported within "Other investments".

[6] Reported within "Other investments"

[7] Reported within “Accrued expenses”.