Fair Value Measurements - Valuation of Company's Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Money market funds	$ 26,627	$ 58,573
Trading securities	78,250	75,534
Assets Fair Value Total	244,093	252,711
Corporate Debt [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale	140,309	118,870
Trading securities	75,404	74,207
Mutual Funds Held In Rabbi Trust [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading securities	2,846	1,327
Foreign Currency Forward Position [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Foreign currency forward position	(1,093)	(266)
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Money market funds	26,627	58,573
Assets Fair Value Total	26,627	58,573
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Fair Value Total	217,466	194,138
Level 2 [Member] | Corporate Debt [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale	140,309	118,870
Trading securities	75,404	74,207
Level 2 [Member] | Mutual Funds Held In Rabbi Trust [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading securities	2,846	1,327
Level 2 [Member] | Foreign Currency Forward Position [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Foreign currency forward position	$ (1,093)	$ (266)