Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	$ 201,536	$ 250,186
Acquisition related contingent consideration		43,486
Repurchase Agreements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	138,931	196,616
Money Markets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	55,043	50,000
Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	7,562	3,570
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	201,536	250,186
Level 2 [Member] | Repurchase Agreements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	138,931	196,616
Level 2 [Member] | Money Markets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	55,043	50,000
Level 2 [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	$ 7,562	3,570
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquisition related contingent consideration		$ 43,486