Investments - Contractual Maturities (Details) (Total available for sale marketable securities [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Total available for sale marketable securities [Member]
Available-for-sale Securities, Schedule of Contractual Maturities [Line Items]
Due in 1 year or less, amortized cost	$ 108,183
Due in 1-5 years, amortized cost	42,014
Available-for-sale securities, amortized cost	150,197	105,659
Due in 1 year or less, fair value	108,191
Due in 1-5 years, fair value	41,991
Available-for-sale securities, fair value	$ 150,182	$ 105,665