Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Assets and liabilities measured at fair value on a recurring basis
Investments held in Rabbi Trusts	$ 32,519	$ 22,426
Interest rate swaps, assets	9,333	15,412
Fair Value, Measurements, Recurring [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	41,852	39,151
Total liabilities at fair value	1,162	478
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	7,101	4,055
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	16,479	10,871
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	4,323	2,974
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	4,616	4,526
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	32,519	22,426
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	7,101	4,055
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	16,479	10,871
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	4,323	2,974
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	4,616	4,526
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	9,333	16,725
Total liabilities at fair value	1,162	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	0	478
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	32,519	22,426
Interest rate swaps, assets	9,333	15,412
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	32,519	22,426
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
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
Fair Value, Measurements, Recurring [Member] | Other noncurrent liabilities [Member]
Assets and liabilities measured at fair value on a recurring basis
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	1,162
Fair Value, Measurements, Recurring [Member] | Other noncurrent liabilities [Member] | Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	0
Fair Value, Measurements, Recurring [Member] | Other noncurrent liabilities [Member] | Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	1,162
Accrued Expenses [Member] | Fair Value, Measurements, Recurring [Member]
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		478
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		$ 478