Acquisitions (Details) (USD $)	12 Months Ended			1 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2011	Dec. 31, 2012	Jan. 31, 2013 NES	Oct. 31, 2013 KVS item	Dec. 31, 2011 Peak
Preliminary Estimates for Allocation of Purchase Price as of Acquisition Date
Consideration paid in cash	$ 119,652,000	$ 65,000,000		$ 37,500,000		$ 65,000,000
Goodwill	512,964,000	501,258,000	472,326,000	15,800,000
Total Consideration					149,000,000
Amount payable in future annual installments to acquire business					66,800,000
Number of annual installments					3
Equity interest acquired (as a percent)						50.00%
Previously held equity interest (as a percent)						50.00%
Previously held equity interest carrying value						$ 38,100,000