Fair Value Measurements (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	$ 35,533	$ 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	4,149	4,055
U.S. Equity Mutual Funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	13,094	10,871
Foreign equity mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	3,417	2,974
Fixed income mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	4,515	4,526
Fair Value, Inputs, Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	25,175	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	4,149	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	13,094	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	3,417	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	4,515	4,526
Fair Value, Inputs, Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	10,358	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] | 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 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	25,175	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	10,358	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	25,175	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	10,358	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
Other noncurrent liabilities [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		478
Other noncurrent liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		0
Other noncurrent liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		0
Other noncurrent liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		$ 478