v3.3.1.900
Shareholders' Equity - Narrative (Details)
 1 Months Ended 12 Months Ended
Nov. 25, 2015
USD ($)
director
$ / shares
shares
Mar. 05, 2015
$ / shares
shares
Feb. 19, 2015
$ / shares
shares
Jan. 01, 2015
$ / shares
shares
Feb. 19, 2014
$ / shares
shares
Aug. 22, 2012
USD ($)
director
$ / shares
shares
Oct. 31, 2013
USD ($)
director
$ / shares
shares
Dec. 31, 2015
USD ($)
$ / shares
shares
Dec. 31, 2014
USD ($)
$ / shares
shares
Dec. 31, 2013
USD ($)
shares
Jul. 24, 2014
USD ($)
Dec. 31, 2012
shares
Class of Stock [Line Items]                        
Shares authorized (in shares) | shares               150,000,000        
Common shares, shares issued (in shares) | shares               74,735,785 73,900,889      
Common shares, shares outstanding (in shares) | shares               73,721,140 72,932,702 72,633,561   72,343,947
Preference shares issued (in shares) | shares               15,900,000        
Shares undesignated (in shares) | shares               59,364,215        
Common shares, par value (in dollars per share)               $ 0.01 $ 0.01      
Number of shares issued (in shares) | shares               378,120 184,396 0    
Proceeds from issuance of Preference Shares | $               $ 159,628,000 $ 0 $ 159,675,000    
Preferred Stock, number of Directors contingently electable | director 2         2            
Preferred Stock, dividend default period           six or more dividend periods            
Shares repurchased (in shares) | shares   33,846 7,658 4,954 5,851     46,458 5,851 0    
Shares repurchased, price per share   $ 14.21 $ 14.40 $ 12.79 $ 11.18              
Preference Shares - Series C                        
Class of Stock [Line Items]                        
Number of shares issued (in shares) | shares 6,600,000                      
Dividend rate of Preference Shares 7.125%                      
Par value of Preference Shares (in dollars per share) $ 0.01                      
Fair value of share (in dollars per share) $ 25                      
Proceeds from issuance of Preference Shares | $ $ 159,628,000                      
Expenses and underwriting discounts | $ $ 5,372,000                      
Redemption price for Preference Shares (in dollars per share) $ 25                      
Shares authorized (in shares) | shares 6,600,000                      
Sale price of Preference Shares (in dollars per share) $ 25                      
Mandatory Convertible Preference Shares - Series B                        
Class of Stock [Line Items]                        
Preference shares offered (in shares) | shares             3,300,000          
Dividend rate of Preference Shares             7.25%          
Par value of Preference Shares (in dollars per share)             $ 0.01          
Fair value of share (in dollars per share)             $ 50          
Proceeds from issuance of Preference Shares | $             $ 159,675,000          
Expenses and underwriting discounts | $             $ 5,325,000          
Shares authorized (in shares) | shares             3,300,000          
Sale price of Preference Shares (in dollars per share)             $ 50          
Liquidation preference per share per annum (in dollars per share)             3.625          
Liquidation preference per share per quarter (in dollars per share)             0.90625          
Liquidation preference per share in initial quarter (in dollars per share)             $ 0.745139          
Convertible Preferred Stock, conversion rate measurement period             40 days          
Preferred Stock, dividend rate (in dollars per share)             $ 0.09          
Dividends on preference shares | $               $ 11,962,000 $ 11,962,000 $ 2,459,000    
Preference shares - Series A                        
Class of Stock [Line Items]                        
Number of shares issued (in shares) | shares           6,000,000            
Dividend rate of Preference Shares           8.25%            
Par value of Preference Shares (in dollars per share)           $ 0.01            
Fair value of share (in dollars per share)           $ 25            
Proceeds from issuance of Preference Shares | $           $ 145,041,000            
Expenses and underwriting discounts | $           $ 4,959,000            
Redemption price for Preference Shares (in dollars per share)           $ 25            
Shares authorized (in shares) | shares           6,000,000            
Sale price of Preference Shares (in dollars per share)           $ 25            
Dividends on preference shares | $               $ 12,375,000 $ 12,375,000 $ 12,375,000    
Maximum                        
Class of Stock [Line Items]                        
Authorized amount of share repurchase program | $                     $ 75,000,000  
Maximum | Mandatory Convertible Preference Shares - Series B                        
Class of Stock [Line Items]                        
Convertible Preferred Stock, shares issued upon conversion ratio             4.0322          
Preferred Stock, number of electable board members | director             2          
Minimum | Mandatory Convertible Preference Shares - Series B                        
Class of Stock [Line Items]                        
Convertible Preferred Stock, shares issued upon conversion ratio             3.2258