Fair Value Measurements (Assets and Liabilities Measured at Fair Value on Non-Recurring Basis) (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities, Fair Value Disclosure, Nonrecurring	$ 0
Assets, Fair Value Disclosure, Nonrecurring	0
Lease impairment obligation		7,400,000
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Lease impairment obligation		0
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Lease impairment obligation		0
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Lease impairment obligation		$ 7,400,000