Fair Value of Financial Instruments (Fair Value Hierarchy) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	$ 105,133	$ 94,843
Level 1 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0	0
Level 2 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	105,133	94,843
Level 3 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0	0
Fair Value | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	105,133	94,843
Commercial paper
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	47,488	32,376
Commercial paper | Level 1 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0	0
Commercial paper | Level 2 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	47,488	32,376
Commercial paper | Level 3 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0	0
Commercial paper | Fair Value | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	47,488	32,376
U.S. government agencies
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	18,837	62,467
U.S. government agencies | Level 1 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0	0
U.S. government agencies | Level 2 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	18,837	62,467
U.S. government agencies | Level 3 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0	0
U.S. government agencies | Fair Value | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	18,837	62,467
Municipal bonds
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	1,128
Municipal bonds | Level 1 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0
Municipal bonds | Level 2 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	1,128
Municipal bonds | Level 3 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0
Municipal bonds | Fair Value | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	1,128
Corporate bonds
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	32,179
Corporate bonds | Level 1 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0
Corporate bonds | Level 2 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	32,179
Corporate bonds | Level 3 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0
Corporate bonds | Fair Value | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	32,179
Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	5,501
Asset-backed securities | Level 1 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0
Asset-backed securities | Level 2 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	5,501
Asset-backed securities | Level 3 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0
Asset-backed securities | Fair Value | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	$ 5,501