Fair Value of Financial Instruments (Cash and Cash Equivalents, Available-for-sale Securities, Restricted Cash Reconciliation) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	$ 132,766	$ 118,424
Unrealized Gains	45	8
Unrealized Losses	(7)	0
Fair value	132,804	118,432
Cash and Cash Equivalents
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents	27,488	23,419
Amortized cost, total	42,368	34,883
Unrealized Gains	1	2
Unrealized Losses	0	0
Fair value	42,369	34,885
Short-term Investments
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	54,810	83,541
Unrealized Gains	17	6
Unrealized Losses	0	0
Fair value	54,827	83,547
Long-Term Investments
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	35,588
Unrealized Gains	27
Unrealized Losses	(7)
Fair value	35,608
Money market funds
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Unrealized Gains	0	0
Unrealized Losses	0	0
Money market funds | Cash and Cash Equivalents
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	183	170
Fair value	183	170
Commercial paper | Cash and Cash Equivalents
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	14,697	11,294
Unrealized Gains	1	2
Unrealized Losses	0	0
Fair value	14,698	11,296
Commercial paper | Short-term Investments
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	32,784	21,078
Unrealized Gains	6	2
Unrealized Losses	0	0
Fair value	32,790	21,080
Corporate bonds | Short-term Investments
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	16,894
Unrealized Gains	11
Unrealized Losses	0
Fair value	16,905
Corporate bonds | Long-Term Investments
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	15,256
Unrealized Gains	22
Unrealized Losses	(4)
Fair value	15,274
Municipal bonds | Short-term Investments
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	1,128
Unrealized Gains	0
Unrealized Losses	0
Fair value	1,128
U.S. government agencies | Short-term Investments
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	4,004	62,463
Unrealized Gains	0	4
Unrealized Losses	0	0
Fair value	4,004	62,467
U.S. government agencies | Long-Term Investments
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	14,835
Unrealized Gains	1
Unrealized Losses	(3)
Fair value	14,833
Asset-backed securities | Long-Term Investments
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	5,497
Unrealized Gains	4
Unrealized Losses	0
Fair value	$ 5,501