Investments (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Short-term investments:
Investments, Cost Basis	$ 133,779	$ 240,273
Available-for-sale Securities, Gross Unrealized Gain	21	2,715
Short-term investments, Fair Value	133,800	242,988
Certificates Of Deposit [Member]
Short-term investments:
Investments, Cost Basis	133,779	215,010
Available-for-sale Securities, Gross Unrealized Gain	21	0
Short-term investments, Fair Value	133,800	215,010
U.S. dollar indexed bond funds [Member]
Short-term investments:
Investments, Cost Basis		25,263
Available-for-sale Securities, Gross Unrealized Gain		2,715
Short-term investments, Fair Value		27,978
Assets held in rabbi trusts [Member]
Long-term investments:
Long-term investments, Cost Basis	9,142	10,085
Long-term investments, Unrealized (Loss) Gain	520	292
Fair Value Of Assets Held Under Trust	$ 9,662	$ 10,377