Fair Value of Financial Instruments (Contractual Maturity) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	$ 69,525	$ 94,843
After One Year through Two Years	30,107	0
Over Two Years	5,501	0
Fair Value	105,133	94,843
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	47,488	32,376
After One Year through Two Years	0	0
Over Two Years	0	0
Fair Value	47,488	32,376
U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	4,004	62,467
After One Year through Two Years	14,833	0
Over Two Years	0	0
Fair Value	18,837	62,467
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	1,128
After One Year through Two Years	0
Over Two Years	0
Fair Value	1,128
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	16,905
After One Year through Two Years	15,274
Over Two Years	0
Fair Value	32,179
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	0
After One Year through Two Years	0
Over Two Years	5,501
Fair Value	$ 5,501