Fair Value Measurements (Details) (Fair Value Measurements Recurring [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Interest rate swaps [Member]
Summary of fair value instruments
Interest rate swaps	$ (9,039)	$ (6,666)
Interest rate swaps [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Summary of fair value instruments
Interest rate swaps	0	0
Interest rate swaps [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Summary of fair value instruments
Interest rate swaps	(9,039)	(6,666)
Interest rate swaps [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Summary of fair value instruments
Interest rate swaps	0	0
Available-for-sale Securities [Member]
Summary of fair value instruments
Available-for-sale securities	3,802	14,168
Available-for-sale Securities [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Summary of fair value instruments
Available-for-sale securities	3,802	14,168
Available-for-sale Securities [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Summary of fair value instruments
Available-for-sale securities	0	0
Available-for-sale Securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Summary of fair value instruments
Available-for-sale securities	0	0
Deferred compensation plan assets [Member]
Summary of fair value instruments
Assets, Fair Value Disclosure	7,973	8,358
Deferred compensation plan assets [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Summary of fair value instruments
Assets, Fair Value Disclosure	0	0
Deferred compensation plan assets [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Summary of fair value instruments
Assets, Fair Value Disclosure	7,973	8,358
Deferred compensation plan assets [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Summary of fair value instruments
Assets, Fair Value Disclosure	0	0
Supplementary pension plan assets [Member]
Summary of fair value instruments
Assets, Fair Value Disclosure	7,632	7,676
Supplementary pension plan assets [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Summary of fair value instruments
Assets, Fair Value Disclosure	0	0
Supplementary pension plan assets [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Summary of fair value instruments
Assets, Fair Value Disclosure	7,632	7,676
Supplementary pension plan assets [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Summary of fair value instruments
Assets, Fair Value Disclosure	$ 0	$ 0

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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Derivative instrument obligations meeting the definition of a liability which the Company is a party to as of the balance sheet date.

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