Employee Incentive Plan (Summary of Partnership Unit Option) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share Based Compenstation Arrangement By Share Based Payment Award Unit Option [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance	37,500	37,500	37,500
Stock Options [Member]
Share Based Compenstation Arrangement By Share Based Payment Award Unit Option [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Beginning Balance			67,500
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period			(30,000)
Unit Options Weighted Average Share Price [Abstract]
Outstanding, beginning of period			$ 9.54
Forfeited			$ 13.33
Outstanding, End of period	$ 6.50	$ 6.50	$ 6.50
Unit Option [Member]
Share Based Compenstation Arrangement By Share Based Payment Award Unit Option [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Beginning Balance	451,574	611,311	882,836
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	(87,857)	(128,477)	(198,725)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period	(14,699)	(31,260)	(67,183)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period	0	0	(5,617)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance	349,018	451,574	611,311
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	286,715	315,742	278,214
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price	$ 7.52	$ 7.42	$ 7.78
Unit Options Weighted Average Share Price [Abstract]
Outstanding, beginning of period	$ 6.99	$ 6.77	$ 6.43
Exercised	$ 4.96	$ 4.61	$ 4.48
Forfeited	$ 13.39	$ 12.83	$ 9.27
Expired	$ 0.00	$ 0.00	$ 5.37
Outstanding, End of period	$ 7.25	$ 6.99	$ 6.77
Weighted Average Contractual Term End Of Period [Abstract]
Options outstanding	6 years 1 month	7 years 2 months	8 years 2 months
Options excercisable	6 years 0 months	6 years 9 months	7 years 6 months
Aggregate Instrinsic Value End Of Period [Abstract]
Options outstanding	$ 3,016	$ 4,648	$ 5,350
Instrinsic value of unit options excerised	$ 2,483	$ 3,260	$ 2,463

Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Number of share options (or share units) exercised during the current period.

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