Fair Value - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 100,331	$ 112,568
Total short-term investments	223,155	210,147
Foreign currency derivatives	1,359	1,431
Total investments	55,184	62,175
Assets, Total	380,029	386,321
Foreign currency derivatives	1,391	1,298
Liabilities, Total	1,391	1,298
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	51,347	51,973
Total investments	17,227	11,818
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	80,834	81,600
Total investments	33,939	36,414
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	53,006	48,762
Government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	29,256	12,684
Total investments		11,944
Other securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	8,712	15,128
Total investments	4,018	1,999
Fair value, measurements, recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	75,637	84,625
Total short-term investments	0	0
Foreign currency derivatives	0	0
Total investments	0	0
Assets, Total	75,637	84,625
Foreign currency derivatives	0	0
Liabilities, Total	0	0
Fair value, measurements, recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	24,694	27,943
Total short-term investments	223,155	210,147
Foreign currency derivatives	1,359	1,431
Total investments	55,184	62,175
Assets, Total	304,392	301,696
Foreign currency derivatives	1,391	1,298
Liabilities, Total	1,391	1,298
Fair value, measurements, recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Total short-term investments	0	0
Foreign currency derivatives	0	0
Total investments	0	0
Assets, Total	0	0
Foreign currency derivatives	0	0
Liabilities, Total	0	0
Fair value, measurements, recurring | Asset-backed securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Total investments	0	0
Fair value, measurements, recurring | Asset-backed securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	51,347	51,973
Total investments	17,227	11,818
Fair value, measurements, recurring | Asset-backed securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Total investments	0	0
Fair value, measurements, recurring | Corporate debt securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Total investments	0	0
Fair value, measurements, recurring | Corporate debt securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	80,834	81,600
Total investments	33,939	36,414
Fair value, measurements, recurring | Corporate debt securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Total investments	0	0
Fair value, measurements, recurring | Commercial paper | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Fair value, measurements, recurring | Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	53,006	48,762
Fair value, measurements, recurring | Commercial paper | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Fair value, measurements, recurring | Government agency securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Total investments		0
Fair value, measurements, recurring | Government agency securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	29,256	12,684
Total investments		11,944
Fair value, measurements, recurring | Government agency securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Total investments		0
Fair value, measurements, recurring | Other securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Total investments	0	0
Fair value, measurements, recurring | Other securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	8,712	15,128
Total investments	4,018	1,999
Fair value, measurements, recurring | Other securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Total investments	$ 0	$ 0