Cash, Cash Equivalents and Short-term Investments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Cash and cash equivalents:
Amortized Cost	$ 39,652	$ 92,520
Unrealized Gains	0	1
Unrealized Losses	0	0
Fair value	39,652	92,521
Short-Term Investments:
Amortized Cost	87,998	34,985
Unrealized Gains	34	4
Unrealized Losses	(8)	0
Fair value	88,024	34,989
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Amortized Cost	127,650	127,505
Unrealized Gains	34	5
Unrealized Losses	(8)	0
Fair value	127,676	127,510
Commercial paper
Short-Term Investments:
Amortized Cost	750	24,987
Unrealized Gains	0	1
Unrealized Losses	0	0
Fair value	750	24,988
U.S. government agency securities
Short-Term Investments:
Amortized Cost	11,275	9,998
Unrealized Gains	5	3
Unrealized Losses	(1)	0
Fair value	11,279	10,001
US Treasury Securities [Member]
Short-Term Investments:
Amortized Cost	5,233
Unrealized Gains	2
Unrealized Losses	0
Fair value	5,235
US States and Political Subdivisions Debt Securities [Member]
Short-Term Investments:
Amortized Cost	4,758
Unrealized Gains	7
Unrealized Losses	0
Fair value	4,765
Corporate Debt Securities [Member]
Short-Term Investments:
Amortized Cost	65,982
Unrealized Gains	20
Unrealized Losses	(7)
Fair value	65,995
Demand deposis and other cash
Cash and cash equivalents:
Amortized Cost	15,451	39,982
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair value	15,451	39,982
Money Market Funds [Member]
Cash and cash equivalents:
Amortized Cost	22,991	45,040
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair value	22,991	45,040
Commercial paper
Cash and cash equivalents:
Amortized Cost	150	7,498
Unrealized Gains	0	1
Unrealized Losses	0	0
Fair value	150	7,499
Corporate Debt Securities [Member]
Cash and cash equivalents:
Amortized Cost	1,060
Unrealized Gains	0
Unrealized Losses	0
Fair value	$ 1,060