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Equity - Reincorporation, Common Stock, Share Repurchase Plan and Preferred Stock (Details)
$ / shares in Units, $ in Millions
 1 Months Ended 12 Months Ended 264 Months Ended
Feb. 28, 2015
$ / shares
Feb. 28, 2014
$ / shares
Jul. 31, 2013
$ / shares
Feb. 28, 2013
$ / shares
Dec. 31, 2015
USD ($)
item
$ / shares
shares
Dec. 31, 2014
USD ($)
$ / shares
shares
Dec. 31, 2013
$ / shares
Dec. 31, 2015
item
$ / shares
shares
Common Stock                
Number of common stock shares authorized | shares         200,000,000 200,000,000   200,000,000
Common stock, par value (in dollars per share) | $ / shares         $ 0.001 $ 0.001   $ 0.001
Votes per share of common stock | item         1     1
Common stock quarterly dividend per share (in dollars per share) | $ / shares $ 0.40 $ 0.35 $ 0.33 $ 0.30   $ 1.40 $ 1.26  
Common stock quarterly dividend per share, before increase (in dollars per share) | $ / shares       $ 0.25        
Share Repurchase Plan                
Stock Repurchase Program, Increase In Number Of Shares Authorized To Be Repurchased | shares         7,500,000      
Repurchase of common shares (in shares) | shares         6,194,641 759,800   22,100,000
Average costs per share | $ / shares         $ 57.39 $ 65.80   $ 30.93
Value of shares repurchased | $         $ 355.5 $ 50.0    
Remaining number of common stock authorized for repurchase under stock repurchase program (in shares) | shares         8,428,592     8,428,592
Preferred Stock                
Preferred stock, authorized shares | shares         5,000,000 5,000,000   5,000,000
Preferred stock, par value (in dollars per share) | $ / shares         $ 0.001 $ 0.001   $ 0.001
Minimum number of series in which preferred shares may be issued | item         1