Fair Value Measurements (Details 1) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Level 1
Fair Value
Cash and Cash Equivalents	$ 21,682	$ 200,526
Short-term Investments	434,803	312,888
Total Cash and Cash Equivalents and Investments	456,485	513,414
Accrued Liabilities	0	0
Other Long-term Liabilities	0	0
Total Liabilities	0	0
Fair Value, Level 2
Fair Value
Cash and Cash Equivalents	2,999	2,463
Short-term Investments	17,662	5,475
Total Cash and Cash Equivalents and Investments	20,661	7,938
Accrued Liabilities	0	0
Other Long-term Liabilities	0	0
Total Liabilities	0	0
Fair Value, Level 3
Fair Value
Cash and Cash Equivalents	0	0
Short-term Investments	0	0
Total Cash and Cash Equivalents and Investments	0	0
Accrued Liabilities	12,979	12,453
Other Long-term Liabilities	10,801	10,362
Total Liabilities	23,780	22,815
Fair Value, Total
Fair Value
Cash and Cash Equivalents	24,681	202,989
Short-term Investments	452,465	318,363
Total Cash and Cash Equivalents and Investments	477,146	521,352
Accrued Liabilities	12,979	12,453
Other Long-term Liabilities	10,801	10,362
Total Liabilities	$ 23,780	$ 22,815