Investments (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Short-term investments:
Investments, Cost Basis	$ 153,236	$ 240,273
Available-for-sale Securities, Gross Unrealized Gain	(266)	2,715
Short-term investments, Fair Value	152,970	242,988
Certificates Of Deposit [Member]
Short-term investments:
Investments, Cost Basis	144,273	215,010
Available-for-sale Securities, Gross Unrealized Gain	0	0
Short-term investments, Fair Value	144,273	215,010
U.S. dollar indexed bond funds [Member]
Short-term investments:
Investments, Cost Basis	8,963	25,263
Available-for-sale Securities, Gross Unrealized Gain	(266)	2,715
Short-term investments, Fair Value	8,697	27,978
Assets held in rabbi trusts [Member]
Long-term investments:
Long-term investments, Cost Basis	9,285	10,085
Long-term investments, Unrealized (Loss) Gain	730	292
Fair Value Of Assets Held Under Trust	$ 10,015	$ 10,377