Derivative Financial Instruments (Narrative) (Details)	12 Months Ended										12 Months Ended
	Dec. 31, 2012 USD ($) integer	Dec. 31, 2011 USD ($) integer	Dec. 31, 2010 USD ($)	Dec. 31, 2012 South African Facility [Member] USD ($) integer	Dec. 31, 2012 South African Facility [Member] ZAR	Sep. 28, 2012 South African Facility [Member] ZAR integer	Aug. 29, 2012 South African Facility [Member] ZAR integer	Jan. 16, 2012 South African Facility [Member] ZAR integer	Dec. 31, 2012 South African Facility [Member] Minimum	Dec. 31, 2012 South African Facility [Member] Maximum	Dec. 31, 2012 Colombian Long-Term Credit Facility [Member] USD ($)	Dec. 31, 2012 Colombian Long-Term Credit Facility [Member] COP	Dec. 05, 2012 Colombian Long-Term Credit Facility [Member] integer
Number of interest rate swap agreements	10	0		9	9	(3)	(3)	(3)					(1)
Aggregate net unrealized gains of approximately	$ (5,315,000)	$ 1,977,000	$ 9,496,000
Net of tax provisions of approximately	700,000	(1,300,000)	(6,000,000)
Other comprehensive loss for change in fair value of interest rate swaps designated as cash flow hedges and reclassified	600,000	100,000	100,000
Net of income tax provisions		100,000	100,000
Notional Amount of Interest Rate Fair Value Hedge Derivatives				49,995,000	423,634,000	12,124,000	61,511,000	350,000,000			57,261,000	101,250,000,000
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, before Tax	(4,800,000)	1,900,000	9,500,000
Reclassifications Due To REIT Conversion	0	(1,752,000)	0
Interest Rate									6.09%	7.25%	5.78%	5.78%
Amount reclassified into earnings over the next 12 months	$ 1,800,000
Derivative, Maturity Date				Mar. 31, 2020	Mar. 31, 2020						Nov. 30, 2020	Nov. 30, 2020