Summary of Significant Accounting Policies (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Assets:
Total	$ 108,721		$ 94,549
Liabilities:
Total	896		1,069
Interest rate swap contracts
Liabilities:
Total	896	[1]	1,069	[1]
Cash and cash equivalents | Money market funds
Assets:
Total	57,879		23,119
Cash and cash equivalents | Commercial paper
Assets:
Total	24,297		38,582
Short-term investments | Commercial paper
Assets:
Total	25,795		32,100
Short-term investments | U.S. government agency bonds
Assets:
Total	750		748
Level 1
Assets:
Total	57,879		23,119
Liabilities:
Total
Level 1 | Interest rate swap contracts
Liabilities:
Total		[1]		[1]
Level 1 | Cash and cash equivalents | Money market funds
Assets:
Total	57,879		23,119
Level 1 | Cash and cash equivalents | Commercial paper
Assets:
Total
Level 1 | Short-term investments | Commercial paper
Assets:
Total
Level 1 | Short-term investments | U.S. government agency bonds
Assets:
Total
Level 2
Assets:
Total	50,842		71,430
Liabilities:
Total	896		1,069
Level 2 | Interest rate swap contracts
Liabilities:
Total	896	[1]	1,069	[1]
Level 2 | Cash and cash equivalents | Money market funds
Assets:
Total
Level 2 | Cash and cash equivalents | Commercial paper
Assets:
Total	24,297		38,582
Level 2 | Short-term investments | Commercial paper
Assets:
Total	25,795		32,100
Level 2 | Short-term investments | U.S. government agency bonds
Assets:
Total	$ 750		$ 748

[1] As of March 31, 2013, the fair value of the interest rate swap contract was classified on our Balance Sheet in “Other current liabilities”. As of December 31, 2012, the fair value of the interest rate swap contracts were classified on our Balance Sheet in “Other non-current liabilities”.