Notes Payable (Details Textual) (Details) (USD $)	6 Months Ended		3 Months Ended		3 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 Line of Credit [Member]	May 28, 2014 Line of Credit [Member]	Jun. 30, 2014 Federal Funds Rate [Member] Line of Credit [Member]	Jun. 30, 2014 Prime Rate [Member] Line of Credit [Member]	Jun. 30, 2014 LIBOR [Member] Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Expansion Amount				$ 250,000,000
Line of Credit Facility, Maximum Borrowing Capacity				750,000,000
Line of Credit Facility, Increase in Borrowing Capacity				150,000,000
Debt Instrument, Fair Value Disclosure	701,200,000	654,100,000
Debt Instrument, Previous Maturity Date			Feb. 28, 2016
Debt Instrument, Maturity Date			May 28, 2019
Unencumbered interest coverage ratio			2.00
Revised Minimum Consolidated Fixed Charge Coverage Ratio			1.50
Line of Credit, Leverage Ratio, Upper Limit			60.00%
Shareholders' Equity, Minimum			1,016,267,000.00
Interest Rate, Credit Facility					federal funds rate	prime rate	LIBOR
Debt Instrument, Basis Spread on Variable Rate					0.50%		1.00%
Line of Credit Facility, Current Borrowing Capacity				500,000,000
Previous Borrowing Capacity Under the Credit Facility				$ 350,000,000
Document Fiscal Year Focus	2014