Fair Value Measurements (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Level 1 [Member]
Assets
Total cash equivalents and investments	$ 73,069	$ 101,839
Level 1 [Member] | Auction Rate Securities [Member]
Assets
Total cash equivalents and investments		1,790
Level 1 [Member] | Money market funds [Member]
Assets
Total cash equivalents and investments	73,069	100,049
Level 1 [Member] | Government-backed security [Member]
Assets
Total cash equivalents and investments
Level 1 [Member] | Asset-backed securities [Member]
Assets
Total cash equivalents and investments
Level 1 [Member] | Corporate Debt Securities [Member]
Assets
Total cash equivalents and investments
Level 2 [Member]
Assets
Total cash equivalents and investments	132,950	26,978
Level 2 [Member] | Auction Rate Securities [Member]
Assets
Total cash equivalents and investments
Level 2 [Member] | Money market funds [Member]
Assets
Total cash equivalents and investments
Level 2 [Member] | Government-backed security [Member]
Assets
Total cash equivalents and investments	18,000
Level 2 [Member] | Asset-backed securities [Member]
Assets
Total cash equivalents and investments	42,483
Level 2 [Member] | Corporate Debt Securities [Member]
Assets
Total cash equivalents and investments	72,467	26,978
Level 3 [Member]
Assets
Total cash equivalents and investments
Level 3 [Member] | Auction Rate Securities [Member]
Assets
Total cash equivalents and investments
Level 3 [Member] | Money market funds [Member]
Assets
Total cash equivalents and investments
Level 3 [Member] | Government-backed security [Member]
Assets
Total cash equivalents and investments
Level 3 [Member] | Asset-backed securities [Member]
Assets
Total cash equivalents and investments
Level 3 [Member] | Corporate Debt Securities [Member]
Assets
Total cash equivalents and investments