Shareholders' Equity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Common shares	Mar. 31, 2014 Additional Paid-In Capital	Mar. 31, 2014 Earnings in Excess of Distributions	Mar. 31, 2014 Accumulated Other Comprehensive Income (Loss)	Mar. 31, 2014 Treasury shares	Mar. 31, 2014 Noncontrolling Interests	Dec. 31, 2013 Stockholders' Equity, Total
Class of Stock [Line Items]
Minimum Percentage Of Taxable Income To Be Distributed As REIT	90.00%
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance	$ 1,023,976		$ 866	$ 848,018	$ 232,646	$ (4,429)	$ (53,579)	$ 454	$ 1,023,976
Beginning Balance, shares			72,082				14,580
Proceeds from exercise of stock options , value	3,275		2	3,273
Proceeds from exercise of stock options , shares	177		177
Tax benefit related to equity compensation	558			558
Stock based compensation expense	452			452
Restricted stock granted, value	0		3	(3)
Restricted stock granted, shares			308
Amortization of restricted stock	2,014			2,014
Dividends paid	(41,139)				(41,139)
Re-issuance of treasury shares (ESPP), value	84			73	0		11
Re-issuance of treasury shares (ESPP), shares			3				(3)
Net income	27,996	23,438			27,990			6
Other comprehensive loss	1,046	(1,180)				1,050		(4)
Ending Balance	$ 1,018,262		$ 871	$ 854,385	$ 219,497	$ (3,379)	$ (53,568)	$ 456	$ 1,023,976
Ending Balance, shares			72,570				14,577