v3.8.0.1
Shareholders' Equity - Narrative (Details) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 9 Months Ended
Jun. 15, 2017
Sep. 30, 2017
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Stockholders' Equity Note [Abstract]          
Common stock, shares authorized (in shares)   150,000,000 150,000,000    
Common stock, shares issued (in shares)   87,728,554 87,728,554   87,321,012
Common stock, shares outstanding (in shares)   84,624,829 84,624,829   86,271,109
Preference shares issued (in shares)   18,600,000 18,600,000    
Preference shares outstanding (in shares)   18,600,000 18,600,000    
Undesignated shares (in shares)   43,671,446 43,671,446    
Class of Stock [Line Items]          
Preference shares, net of issuance costs     $ 144,942 $ 0  
Shares repurchased (in shares)   2,015,700 2,015,700    
Shares repurchased, price per share (in dollars per share)   $ 7.11 $ 7.11    
Remaining authorization for share repurchase   $ 85,662 $ 85,662    
Shares repurchased for tax withholding (in shares)   0 38,122    
Shares repurchased for tax withholding, price per share (in dollars per share)     $ 15.06    
Preference shares - Series D [Member]          
Class of Stock [Line Items]          
Number of shares issued (in shares) 6,000,000        
Dividend rate of Preference Shares 6.70%        
Shares authorized (in shares) 6,000,000        
Par value of Preference Shares (in dollars per share) $ 0.01        
Fair value of share (in dollars per share) $ 25        
Preference shares, net of issuance costs $ 144,942        
Expenses and underwriting discounts $ 5,058        
Redemption price for Preference Shares (in dollars per share) $ 25        
Redemption price, prior to June 15, 2022 (in dollars per share) $ 26