Comprehensive Income (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 Interest Rate Derivatives [Member]	Jun. 30, 2010 Interest Rate Derivatives [Member]	Mar. 31, 2010 Interest Rate Derivatives [Member]	Dec. 31, 2009 Interest Rate Derivatives [Member]
Notional amount of interest rate swaps							$ 30,000,000	$ 60,000,000
LIBOR average fixed interest rate							1.45%	1.83%
Interest expense	1,911,000	3,508,000	3,751,000	6,986,000	700,000	4,200,000
Ineffectiveness related to hedges						0
Liability related to interest rate derivatives					1,100,000
Unrealized gain on interest rate derivatives	80,000	769,000	212,000	1,563,000	200,000
Income tax expense	7,645,000	5,904,000	14,132,000	10,770,000	200,000
Accumulated other comprehensive income (loss) related to foreign currency translation loss	(8,100,000)		(8,100,000)
Accumulated other comprehensive income (loss) related to interest rate derivatives					$ (700,000)