Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	$ 40,396	$ 40,539
Total liabilities at fair value		1,000
Cash and Cash Equivalents [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	3,334	3,783
U.S. Equity Mutual Funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	10,224	8,850
Foreign equity mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	2,653	2,526
Fixed income mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	4,294	3,537
Fair Value, Inputs, Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	20,505	18,696
Total liabilities at fair value		0
Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	3,334	3,783
Fair Value, Inputs, Level 1 [Member] | U.S. Equity Mutual Funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	10,224	8,850
Fair Value, Inputs, Level 1 [Member] | Foreign equity mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	2,653	2,526
Fair Value, Inputs, Level 1 [Member] | Fixed income mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	4,294	3,537
Fair Value, Inputs, Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	19,891	21,843
Total liabilities at fair value		0
Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	0	0
Fair Value, Inputs, Level 2 [Member] | U.S. Equity Mutual Funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	0	0
Fair Value, Inputs, Level 2 [Member] | Foreign equity mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	0	0
Fair Value, Inputs, Level 2 [Member] | Fixed income mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	0	0
Fair Value, Inputs, Level 3 [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	0	0
Total liabilities at fair value		1,000
Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	0	0
Fair Value, Inputs, Level 3 [Member] | U.S. Equity Mutual Funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	0	0
Fair Value, Inputs, Level 3 [Member] | Foreign equity mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	0	0
Fair Value, Inputs, Level 3 [Member] | Fixed income mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	0	0
Prepaid Expenses and Other Current Assets [Member] | Interest rate swap [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest rate swaps, assets	5,123
Prepaid Expenses and Other Current Assets [Member] | Fair Value, Inputs, Level 1 [Member] | Interest rate swap [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest rate swaps, assets	0
Prepaid Expenses and Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member] | Interest rate swap [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest rate swaps, assets	5,123
Prepaid Expenses and Other Current Assets [Member] | Fair Value, Inputs, Level 3 [Member] | Interest rate swap [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest rate swaps, assets	0
Direct Financing Leases and Other Assets [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	20,505	18,696
Direct Financing Leases and Other Assets [Member] | Interest rate swap [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest rate swaps, assets	14,768	21,843
Direct Financing Leases and Other Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	20,505	18,696
Direct Financing Leases and Other Assets [Member] | Fair Value, Inputs, Level 1 [Member] | Interest rate swap [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest rate swaps, assets	0	0
Direct Financing Leases and Other Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	0	0
Direct Financing Leases and Other Assets [Member] | Fair Value, Inputs, Level 2 [Member] | Interest rate swap [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest rate swaps, assets	14,768	21,843
Direct Financing Leases and Other Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	0	0
Direct Financing Leases and Other Assets [Member] | Fair Value, Inputs, Level 3 [Member] | Interest rate swap [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest rate swaps, assets	0	0
Accrued Expenses [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		1,000
Accrued Expenses [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		0
Accrued Expenses [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		0
Accrued Expenses [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		$ 1,000