Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	$ 22,426	$ 18,696
Interest rate swaps, assets	15,412	21,843
Fair Value, Measurements, Recurring [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	39,151	40,539
Total liabilities at fair value	478	1,000
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	4,055	3,783
Fair Value, Measurements, Recurring [Member] | U.S. Equity Mutual Funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	10,871	8,850
Fair Value, Measurements, Recurring [Member] | Foreign equity mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	2,974	2,526
Fair Value, Measurements, Recurring [Member] | Fixed income mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	4,526	3,537
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	22,426	18,696
Total liabilities at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Cash and Cash Equivalents [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	4,055	3,783
Fair Value, Measurements, Recurring [Member] | 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	10,871	8,850
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Foreign equity mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	2,974	2,526
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Fixed income mutual funds [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	4,526	3,537
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	16,725	21,843
Total liabilities at fair value	0	0
Fair Value, Measurements, Recurring [Member] | 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, Measurements, Recurring [Member] | 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, Measurements, Recurring [Member] | 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, Measurements, Recurring [Member] | 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, Measurements, Recurring [Member] | 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	1,000
Fair Value, Measurements, Recurring [Member] | 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, Measurements, Recurring [Member] | 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, Measurements, Recurring [Member] | 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, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | Prepaid Expenses and Other Current Assets [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest rate swaps, assets	1,313
Fair Value, Measurements, Recurring [Member] | Prepaid Expenses and Other Current Assets [Member] | Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest rate swaps, assets	0
Fair Value, Measurements, Recurring [Member] | Prepaid Expenses and Other Current Assets [Member] | Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest rate swaps, assets	1,313
Fair Value, Measurements, Recurring [Member] | Prepaid Expenses and Other Current Assets [Member] | Level 3 [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest rate swaps, assets	0
Fair Value, Measurements, Recurring [Member] | Direct Financing Leases and Other Assets [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	22,426	18,696
Interest rate swaps, assets	15,412	21,843
Fair Value, Measurements, Recurring [Member] | Direct Financing Leases and Other Assets [Member] | Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts		18,696
Interest rate swaps, assets	0	0
Fair Value, Measurements, Recurring [Member] | Direct Financing Leases and Other Assets [Member] | Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	0	0
Interest rate swaps, assets	15,412	21,843
Fair Value, Measurements, Recurring [Member] | Direct Financing Leases and Other Assets [Member] | Level 3 [Member]
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	0	0
Interest rate swaps, assets	0	0
Other noncurrent liabilities [Member] | Fair Value, Measurements, Recurring [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration	478
Other noncurrent liabilities [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration	0
Other noncurrent liabilities [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration	0
Other noncurrent liabilities [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration	478
Accrued Expenses [Member] | Fair Value, Measurements, Recurring [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		1,000
Accrued Expenses [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		0
Accrued Expenses [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		0
Accrued Expenses [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		$ 1,000