Derivative Financial Instruments (Details)	6 Months Ended						6 Months Ended
	Jun. 30, 2013 USD ($)	Jun. 30, 2013 Interest rate swap, variable rate, secured debt Interest rate swap, entered in July 2005, maturity in July 2020 USD ($) item	Jun. 30, 2013 Interest rate swap, variable rate, secured debt Interest rate swap, entered in November 2008, maturity in October 2016 USD ($)	Jun. 30, 2013 Interest rate swap, variable rate, secured debt Interest rate swap, entered in July 2009, maturity in July 2013 USD ($)	Jun. 30, 2013 Interest rate swap, variable rate, secured debt Interest rate swap, entered in July 2012, maturity in June 2016 USD ($)	Jun. 30, 2013 Interest rate swap, variable rate, secured debt Interest rate swap, entered in July 2012, maturity in June 2016 GBP (£)	Jun. 30, 2013 Foreign currency swap contract Foreign currency swap, entered in July 2012, maturity in June 2016 USD ($) item	Jun. 30, 2013 Foreign currency swap contract Foreign currency swap, entered in July 2012, maturity in June 2016 GBP (£)
Derivative
Fixed Rate/Buy Amount (as a percent)		3.82%	5.95%	6.13%	1.81%
Floating/Exchange Rate Index		BMA Swap Index	1 Month LIBOR	1 Month LIBOR	1 Month GBP LIBOR
Floating/Exchange Rate Index, percentage			1.50%	3.65%	1.20%
Notional / Sell Amount		$ 45,600,000	$ 26,700,000	$ 13,500,000		£ 137,000,000
Notional amount of foreign currency derivative purchase contracts							68,200,000
Notional amount of foreign currency derivative sale contracts								43,500,000
Semi-annual buy (sell) amount							11,400,000	(7,200,000)
Fair value of hedge, liabilities		(6,496,000)	(3,113,000)	(1,000)
Number of interest-rate swap contracts		3
Exchange rate USD/GBP							1.5695
Number of foreign exchange contracts							6
Fair value of hedge, assets					1,487,000		2,218,000
Gain (loss) on cash flow hedge, ineffective portion					0		0
Gains or losses recorded to accumulated other comprehensive loss reclassified to earnings	0
Effects of Change in Interest Rates
+50 Basis Points		1,512,000	439,000	(1,000)	2,898,000		(459,000)
-50 Basis Points		(1,490,000)	(411,000)	(2,000)	(3,209,000)		202,000
+100 Basis Points		3,013,000	864,000	(1,000)	5,951,000		(790,000)
-100 Basis Points		$ (2,991,000)	$ (836,000)	$ (3,000)	$ (6,263,000)		$ 532,000