Fair Value Measurements - Financial assets measured at fair value on a recurring basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Cash, including short-term deposits [Member]
Financial Assets	$ 94,200	[1]	$ 68,265	[1]
Cash, including short-term deposits [Member] | Cash And Cash Equivalent [Member]
Financial Assets	94,100		68,200
Cash, including short-term deposits [Member] | Marketable Securities [Member]
Financial Assets	100		100
Cash, including short-term deposits [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets	94,200	[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]
US Government Agencies Debt Securities [Member] | Cash And Cash Equivalent [Member]
Financial Assets	500
US Government Agencies Debt Securities [Member] | Marketable Securities [Member]
Financial Assets	49,100
Mutual Funds [Member]
Financial Assets	13,889	[2]	11,820	[2]
Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets	13,889	[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	49,549	[3]	99,477	[2]
US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets	49,549	[3]	99,477	[2]
US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets	0	[3]	0	[2]
US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets	0	[3]	0	[2]
Corporate Securities [Member]
Financial Assets	67,128	[2]	20,117	[2]
Corporate Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets	58,889	[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	8,239	[2]	0	[2]
Commercial Paper [Member]
Financial Assets	9,796	[4]	22,291	[5]
Commercial Paper [Member] | Cash And Cash Equivalent [Member]
Financial Assets	3,600		3,400	[2]
Commercial Paper [Member] | Marketable Securities [Member]
Financial Assets	6,200		18,900	[2]
Commercial Paper [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets	0	[4]	0	[5]
Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets	9,796	[4]	22,291	[5]
Commercial Paper [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets	0	[4]	0	[5]
Corporate Obligations [Member]
Financial Assets	24,098	[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	12,400	[2]	46,931	[2]
Corporate Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets	11,698	[2]	1,783	[2]
Non-controlling interests in certain funds [Member]
Financial Assets	1,015	[6]	1,021	[6]
Non-controlling interests in certain funds [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets	0	[6]	0	[6]
Non-controlling interests in certain funds [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets	0	[6]	0	[6]
Non-controlling interests in certain funds [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets	1,015	[6]	1,021	[6]
Financial Assets [Member]
Financial Assets	259,675		271,705
Financial Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets	216,527		199,679
Financial Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets	22,196		69,222
Financial Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets	20,952		2,804
Acquisition-related contingent consideration [Member]
Financial Liabilities	(475)	[7]	(475)	[7]
Acquisition-related contingent consideration [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Liabilities		[7]	0	[7]
Acquisition-related contingent consideration [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Liabilities		[7]	0	[7]
Acquisition-related contingent consideration [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Liabilities	$ (475)	[7]	$ (475)

[1] At June 30, 2013, the Company reported $94.1 million and $0.1 million within “Cash and cash equivalents” and “Marketable securities,” respectively.

[2] Reported within “Marketable securities.”

[3] At June 30, 2013, the Company reported $0.5 million and $49.1 million within "Cash and cash equivalents" and "Marketable securities," respectively.

[4] At June 30, 2013, the Company reported $3.6 million and $6.2 million within "Cash and cash equivalents" and "Marketable securities," respectively.

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

[6] Reported within “Other long-term assets.”

[7] Reported within “Other long-term liabilities.”