Quarterly report pursuant to Section 13 or 15(d)

Shareholders' Equity (Details)

Shareholders' Equity (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
0 Months Ended 3 Months Ended
Mar. 19, 2013
Mar. 31, 2013
Mar. 31, 2012
Common Shares      
Shares issued to the public (in shares) 4,485,000    
Shares issued to the public (in dollars per share) $ 26.34    
Public Offering, Proceeds After Underwriter Discounts But Before Offering Expenses $ 118,100 $ 117,913  
Number of operating parterships units converted into common shares (in units)   248,644 34,550
Number of common shares for each converted common unit (in shares)   1