Fair Value Measurements (Details 1) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Level 1
Fair Value
Cash and Cash Equivalents	$ 38,410	$ 200,526
Short-term Investments	379,640	312,888
Total Cash and Cash Equivalents and Investments	418,050	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	0	2,463
Short-term Investments	11,315	5,475
Total Cash and Cash Equivalents and Investments	11,315	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	13,396	12,453
Other Long-term Liabilities	10,862	10,362
Total Liabilities	24,258	22,815
Fair Value, Total
Fair Value
Cash and Cash Equivalents	38,410	202,989
Short-term Investments	390,955	318,363
Total Cash and Cash Equivalents and Investments	429,365	521,352
Accrued Liabilities	13,396	12,453
Other Long-term Liabilities	10,862	10,362
Total Liabilities	$ 24,258	$ 22,815