Total Debt (Details) (USD $)	12 Months Ended									0 Months Ended	12 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Unsecured Debt [Member]	Dec. 31, 2012 Unsecured Debt [Member]	Dec. 31, 2013 Secured Debt [Member]	Dec. 31, 2012 Secured Debt [Member]	Dec. 31, 2013 Revolving Credit Facility [Member]	Dec. 31, 2012 Revolving Credit Facility [Member]	May 17, 2013 Revolving Credit Facility [Member] London Interbank Offered Rate (LIBOR) [Member]	Dec. 31, 2013 Revolving Credit Facility [Member] London Interbank Offered Rate (LIBOR) [Member]	Oct. 31, 2010 Revolving Credit Facility [Member] London Interbank Offered Rate (LIBOR) [Member]	Dec. 31, 2013 Revolving Credit Facility [Member] London Interbank Offered Rate (LIBOR) [Member] Minimum	Dec. 31, 2013 Revolving Credit Facility [Member] London Interbank Offered Rate (LIBOR) [Member] Maximum	Dec. 31, 2013 Line of Credit [Member]	Dec. 31, 2012 Line of Credit [Member]
Debt Instrument [Line Items]
Total long-term debt	$ 369,191,000	$ 0		$ 300,000,000	$ 0	$ 58,000,000	$ 0		$ 205,000,000						$ 11,191,000	$ 0
Debt Instrument, Interest Rate, Stated Percentage	5.375%
Proceeds from Issuance of Unsecured Debt	295,000,000
Debt Issuance Cost	6,300,000
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed	104.031%
Current maturities of long-term debt	0	209,728,000						0							0	4,728,000
Total debt	369,191,000	209,728,000
Debt instrument, face amount										500,000,000		375,000,000
Loan origination fees	(2,258,000)	(67,000)	(155,000)
Amendment, decrease in pricing schedule												0.375%
Amendment, decrease in commitment fee												0.05%
Variable rate basis											LIBOR
Margin on variable rate													1.125%	3.00%
Commitment fee, unused capacity													0.175%	0.45%
Debt, Weighted Average Interest Rate	1.71%	1.87%
Debt covenant, interest coverage ratio													3.0
Debt covenant, leverage ratio													4.5	5.0
Line of Credit Facility, Covenant Terms,SeniorSecuredLeverage Ratio														3.5
Remaining borrowing capacity											425,000,000
Interest Expense	6,231,000	4,531,000	8,924,000
Debt Instrument additional amount										225,000,000
Payments of Financing Costs										$ 2,300,000