Revolving Credit Facilities, Term Loan, and the Notes (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2013 item
Aggregate maturities of long-term debt including future interest for each of the five years
Total	$ 712,774,000
Year 1	40,219,000
Year 2	40,100,000
Year 3	40,049,000
Year 4	39,960,000
Year 5	39,890,000
Thereafter	512,556,000
Guarantees
Amount of independent assets	0
Amount of independent operations	0
Number of subsidiaries that are not guarantors	0
Notes, due July 15, 2019
Aggregate maturities of long-term debt including future interest for each of the five years
Total	504,750,000
Year 1	31,500,000
Year 2	31,500,000
Year 3	31,500,000
Year 4	31,500,000
Year 5	31,500,000
Thereafter	347,250,000
Term Loan, due July 14, 2018
Aggregate maturities of long-term debt including future interest for each of the five years
Total	208,024,000
Year 1	8,719,000
Year 2	8,600,000
Year 3	8,549,000
Year 4	8,460,000
Year 5	8,390,000
Thereafter	$ 165,306,000