Debt, Continued (Narrative) (Details) (USD $) In Thousands, unless otherwise specified					0 Months Ended	3 Months Ended				3 Months Ended			3 Months Ended			2 Months Ended	3 Months Ended	2 Months Ended	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Minimum [Member]	Mar. 31, 2014 Maximum [Member]	Feb. 27, 2014 Senior Unsecured Credit Agreement [Member]	Mar. 31, 2014 Senior Unsecured Credit Agreement [Member]	Mar. 31, 2014 Unsecured Term Loan [Member]	Feb. 27, 2014 Unsecured Term Loan [Member]	Dec. 31, 2013 Unsecured Term Loan [Member]	Mar. 31, 2014 Unsecured Term Loan [Member] Minimum [Member]	Mar. 31, 2014 Unsecured Term Loan [Member] Maximum [Member]	Feb. 27, 2014 Secured Credit Facility [Member]	Mar. 31, 2014 Revolving Line Of Credit [Member]	Mar. 31, 2013 Revolving Line Of Credit [Member]	Feb. 27, 2014 Revolving Line Of Credit [Member]	Feb. 27, 2014 Revolving Line Of Credit [Member] Minimum [Member]	Mar. 31, 2014 Revolving Line Of Credit [Member] Minimum [Member]	Feb. 27, 2014 Revolving Line Of Credit [Member] Maximum [Member]	Mar. 31, 2014 Revolving Line Of Credit [Member] Maximum [Member]
Revolving Line of Credit [Abstract]
Revolving line of credit, current borrowing capacity					$ 400,000	$ 500,000	$ 250,000	$ 150,000					$ 250,000		$ 250,000
Revolving line of credit, maximum borrowing capacity					550,000	850,000						250,000
Line of credit, expiration date					Nov. 05, 2015	Feb. 28, 2018
Renewal period of line of credit					1 year	1 year
Interest rate on loans provided under line of credit													The interest rate for the $500,000 unsecured credit facility is based on a pricing grid with a range of one month U.S. LIBOR plus 1.70% to 2.45% for the revolving line of credit and 1.60% to 2.35% for the unsecured term loan.
Description of variable rate basis													one month U.S. LIBOR
Fixed interest rate																	3.217%
Basis spread on variable rate (in hundredths)										1.60%	2.35%					1.75%	1.70%	2.65%	2.45%
Line of credit, financial covenant terms													The credit agreement providing for the $500,000 unsecured credit facility includes certain financial covenants and requires that we maintain: (1) a minimum tangible net worth of $803,711, plus an amount equal to 75% times the net cash proceeds of all issuances and primary sales of equity interests of the parent guarantor or any of its subsidiaries consummated following the closing date; (2) annual distributions not to exceed 95% of adjusted funds from operations; and (3) certain financial ratios, including the following:· a fixed charge coverage ratio of not less than 1.45 to 1.00, which increases to 1.50 to 1.00 as of January 1, 2016;· a maximum leverage ratio of not more than 60%; and· a maximum secured debt leverage ratio of 50%, which decreases to 45% as of January 1, 2016.The Company is in compliance with each of the covenants listed above as of March 31, 2014.
Line of credit facility covenant minimum tangible net worth	803,711
Line of credit facility covenant maximum annual distributions (in hundredths)	95.00%
Line of credit facility covenant fixed charge coverage ratio	1.45	1.50
Line of credit facility covenant maximum leverage ratio (in hundredths)	60.00%
Line of credit facility covenant maximum secured debt leverage ratio (in hundredths)			45.00%	50.00%
Line of credit, remaining borrowing capacity													322,745
Line of credit, outstanding principal balance							150,000		150,000
Outstanding borrowings on revoloving line of credit	23,000
Interest Expense, on credit facilities													$ 1,103	$ 1,063
Line of credit, weighted average interest rate (in hundredths)													3.14%	3.25%