Summary of Significant Accounting Policies (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Assets:
Total	$ 161,541	$ 94,549
Liabilities:
Total	154	1,069
Interest rate swap contracts
Liabilities:
Total	154	1,069
Level 1
Assets:
Total	13,761	23,119
Level 2
Assets:
Total	147,780	71,430
Liabilities:
Total	154	1,069
Level 2 | Interest rate swap contracts
Liabilities:
Total	154	1,069
Cash equivalents | Money market funds
Assets:
Total	13,761	23,119
Cash equivalents | Money market funds | Level 1
Assets:
Total	13,761	23,119
Cash equivalents | Commercial paper
Assets:
Total	19,629	35,856
Cash equivalents | Commercial paper | Level 2
Assets:
Total	19,629	35,856
Short-term Investments | Municipal bonds
Assets:
Total	29,106
Short-term Investments | Corporate debt securities
Assets:
Total	76,786	34,826
Short-term Investments | Asset-backed securities
Assets:
Total	4,209
Short-term Investments | Level 2 | Municipal bonds
Assets:
Total	29,106
Short-term Investments | Level 2 | Corporate debt securities
Assets:
Total	76,786	34,826
Short-term Investments | Level 2 | Asset-backed securities
Assets:
Total	4,209
Short-term Investments | U.S. government agency bonds
Assets:
Total	18,050	748
Short-term Investments | U.S. government agency bonds | Level 2
Assets:
Total	$ 18,050	$ 748