Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	$ 37,567	$ 39,151
Total liabilities at fair value	478	478
Cash and Cash Equivalents [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	3,513	4,055
U.S. Equity Mutual Funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	12,239	10,871
Foreign equity mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	3,337	2,974
Fixed income mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	4,534	4,526
Fair Value, Inputs, Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	23,623	22,426
Total liabilities at fair value	0	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	3,513	4,055
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	12,239	10,871
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	3,337	2,974
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	4,534	4,526
Fair Value, Inputs, Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	13,944	16,725
Total liabilities at fair value	0	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	478	478
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] | 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		1,313
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	23,623	22,426
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	13,944	15,412
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	23,623	22,426
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	13,944	15,412
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 Liabilities [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		478
Accrued Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		0
Accrued Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		0
Accrued Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		478
Accrued Expenses [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration	478
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	$ 478