Fair Value Measurements (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Additional obligations	$ 8,680,000	$ 4,824,000
Senior subordinated notes	200,000,000	200,000,000
Fair value of senior subordinated notes	217,500,000
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Additional obligations	8,700,000	4,800,000	3,100,000
Interest Rate Swap Contracts [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Company's interest rate swaps	$ 70,500,000