Derivative Financial Instruments (Details)	3 Months Ended		9 Months Ended							9 Months Ended
	Sep. 30, 2013 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2013 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2013 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges Reclassification out of Accumulated Other Comprehensive Income USD ($)	Sep. 30, 2013 Interest rate swap, entered in July 2005, maturity in July 2020 Cash flow hedge USD ($) item	Sep. 30, 2013 Interest rate swap, entered in November 2008, maturity in October 2016 Cash flow hedge USD ($)	Sep. 30, 2013 Interest rate swap, entered in July 2012, maturity in June 2016 Cash flow hedge USD ($)	Sep. 30, 2013 Interest rate swap, entered in July 2012, maturity in June 2016 Cash flow hedge GBP (£)	Sep. 30, 2013 Foreign currency swap, entered in July 2012, maturity in June 2016 Cash flow hedge USD ($) item	Sep. 30, 2013 Foreign currency swap, entered in July 2012, maturity in June 2016 Cash flow hedge GBP (£)
Derivative
Fixed Rate/Buy Amount (as a percent)						3.82%	5.95%	1.81%
Floating/Exchange Rate Index						BMA Swap Index	1 Month LIBOR	1 Month GBP LIBOR
Floating/Exchange Rate Index, percentage							1.50%	1.20%
Buy (sell) amount										$ 68,200,000
Notional amount						45,600,000	26,600,000		137,000,000		43,500,000
Semi-annual buy (sell) amount										11,400,000	(7,200,000)
Fair value of hedge, liabilities						(6,319,000)	(2,964,000)
Fair value of hedge, liabilities										(1,897,000)
Number of interest-rate swap contracts						3
Exchange rate USD/GBP										1.5695
Number of foreign exchange contracts										6
Fair value of hedge, assets								1,564,000
Gain (loss) on cash flow hedge, ineffective portion								0		0
Gains or losses recorded to accumulated other comprehensive loss reclassified to earnings	236,858,000	199,043,000	687,367,000	600,582,000	0
Effects of Change in Interest Rates
+50 Basis Points						1,442,000	404,000	3,038,000		(580,000)
-50 Basis Points						(1,455,000)	(379,000)	(2,902,000)		123,000
+100 Basis Points						2,890,000	796,000	6,008,000		(932,000)
-100 Basis Points						$ (2,904,000)	$ (770,000)	$ (5,872,000)		$ 475,000