Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fair Value, Level 1
Fair Value
Cash and cash equivalents	$ 23,254	$ 30,423
Short-term investments	152,124	192,785
Total cash and cash equivalents and investments	175,378	223,208
Other long-term liabilities	0	0
Total liabilities	0	0
Fair Value, Level 2
Fair Value
Cash and cash equivalents	0	0
Short-term investments	0	0
Total cash and cash equivalents and investments	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
Other long-term liabilities	31,661	29,920
Total liabilities	31,661	29,920
Fair Value, Total
Fair Value
Cash and cash equivalents	23,254	30,423
Short-term investments	152,124	192,785
Total cash and cash equivalents and investments	175,378	223,208
Other long-term liabilities	31,661	29,920
Total liabilities	$ 31,661	$ 29,920