Fair Value of Financial Instruments (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value Disclosures
Marketable Securities	$ 271,539	$ 95,313
Recurring basis | Fair Value Measurement Using: Level 2
Fair Value Disclosures
Marketable Securities	256,089	83,114
Total assets	256,089	83,114
Recurring basis | Fair Value Measurement Using: Level 3
Fair Value Disclosures
Marketable Securities		952
Total assets		952
Recurring basis | Assets at Fair Value
Fair Value Disclosures
Marketable Securities	256,089	84,066
Total assets	$ 256,089	$ 84,066