Summary of Significant Accounting Policies (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Assets:
Total	$ 108,879	$ 94,069
Liabilities:
Total	1,164	1,005
Interest rate swap contracts [Member]
Liabilities:
Total	1,164	1,005
Cash and cash equivalents [Member] | Money market funds [Member]
Assets:
Total	80,781	77,174
Cash and cash equivalents [Member] | Commercial paper [Member]
Assets:
Total	7,999	4,798
Short-term investments [Member] | Commercial paper [Member]
Assets:
Total	15,744	12,097
Short-term investments [Member] | U.S. government agency bonds [Member]
Assets:
Total	4,355
Level 1 [Member]
Assets:
Total	80,781	77,174
Liabilities:
Total
Level 1 [Member] | Interest rate swap contracts [Member]
Liabilities:
Total
Level 1 [Member] | Cash and cash equivalents [Member] | Money market funds [Member]
Assets:
Total	80,781	77,174
Level 1 [Member] | Cash and cash equivalents [Member] | Commercial paper [Member]
Assets:
Total
Level 1 [Member] | Short-term investments [Member] | Commercial paper [Member]
Assets:
Total
Level 1 [Member] | Short-term investments [Member] | U.S. government agency bonds [Member]
Assets:
Total
Level 2 [Member]
Assets:
Total	28,098	16,895
Liabilities:
Total	1,164	1,005
Level 2 [Member] | Interest rate swap contracts [Member]
Liabilities:
Total	1,164	1,005
Level 2 [Member] | Cash and cash equivalents [Member] | Money market funds [Member]
Assets:
Total
Level 2 [Member] | Cash and cash equivalents [Member] | Commercial paper [Member]
Assets:
Total	7,999	4,798
Level 2 [Member] | Short-term investments [Member] | Commercial paper [Member]
Assets:
Total	15,744	12,097
Level 2 [Member] | Short-term investments [Member] | U.S. government agency bonds [Member]
Assets:
Total	$ 4,355