Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
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	$ 2,509
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 3 [Member] | Interest rate swap [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest rate swaps, assets	0
Fair Value, Measurements, Recurring [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	41,241	41,852
Total liabilities at fair value	1,946	1,162
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	3,719	7,101
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	20,005	16,479
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	4,383	4,323
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	5,000	4,616
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	33,107	32,519
Total liabilities at fair value	0	0
Fair Value, Measurements, Recurring [Member] | 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	3,719	7,101
Fair Value, Measurements, Recurring [Member] | 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	20,005	16,479
Fair Value, Measurements, Recurring [Member] | 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	4,383	4,323
Fair Value, Measurements, Recurring [Member] | 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	5,000	4,616
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Total assets at fair value	8,134	9,333
Total liabilities at fair value	1,946	1,162
Fair Value, Measurements, Recurring [Member] | 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, Measurements, Recurring [Member] | 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, Measurements, Recurring [Member] | 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, Measurements, Recurring [Member] | 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, Measurements, Recurring [Member] | 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	0	0
Fair Value, Measurements, Recurring [Member] | 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, Measurements, Recurring [Member] | 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, Measurements, Recurring [Member] | 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, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | 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	2,509
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	33,107	32,519
Fair Value, Measurements, Recurring [Member] | 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	5,625	9,333
Fair Value, Measurements, Recurring [Member] | 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	33,107	32,519
Fair Value, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | 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	5,625	9,333
Fair Value, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | Accrued Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest Rate Derivative Liabilities, at Fair Value	0
Fair Value, Measurements, Recurring [Member] | Accrued Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest Rate Derivative Liabilities, at Fair Value	0
Fair Value, Measurements, Recurring [Member] | Other noncurrent liabilities [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest Rate Derivative Liabilities, at Fair Value	1,946	1,162
Fair Value, Measurements, Recurring [Member] | Other noncurrent liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest Rate Derivative Liabilities, at Fair Value		0
Fair Value, Measurements, Recurring [Member] | Other noncurrent liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest Rate Derivative Liabilities, at Fair Value	1,946	1,162
Fair Value, Measurements, Recurring [Member] | Other noncurrent liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and liabilities measured at fair value on a recurring basis
Interest Rate Derivative Liabilities, at Fair Value		$ 0