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Stockholders' Equity - Restricted Stock Plan (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock award, issued during period (in shares) 1,294,136      
Restricted Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based payment award, number of shares authorized (in shares)       5,000,000
Share-based payment award, limitation on single participant (in shares) (no more than)       750,000
Restricted stock award, not yet vested (in shares) 366,363 318,561 433,382 197,674
Unrecognized compensation expense       $ 2.2
Unrecognized compensation expense, recognition weighted average period 1 year 11 months      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]        
Nonvested restricted shares outstanding at beginning of year (in shares) 366,363 318,561 433,382  
Nonvested restricted shares granted (in shares) 107,346 201,680 274,172  
Nonvested restricted shares forfeited (in shares) (39,322) (675) (42,711)  
Nonvested restricted shares vested (in shares) (236,713) (153,203) (346,282)  
Nonvested restricted shares outstanding at end of year (in shares) 197,674 366,363 318,561  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]        
Weighted Average Grant Date Fair Value, Outstanding at beginning of year (in dollars per share) $ 38.24 $ 35.82 $ 18.94  
Weighted Average Grant Date Fair Value, Granted (in dollars per share) 45.34 39.55 36.47  
Weighted Average Grant Date Fair Value, Forfeited (in dollars per share) 40.93 48.68 33.71  
Weighted Average Grant Date Fair Value, Vested (in dollars per share) 36.57 34.89 15.33  
Weighted Average Grant Date Fair Value, Outstanding at end of year (in dollars per share) $ 43.56 $ 38.24 $ 35.82  
Restricted Stock Performance Plan [Member] | Award Opportunity 2015-2016 [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]        
Nonvested restricted shares granted (in shares) 71,228      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]        
Compensation expense $ 1.8      
Restricted Stock Performance Plan [Member] | Award Opportunity 2014-2015 [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]        
Nonvested restricted shares granted (in shares)   43,842    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]        
Compensation expense $ 0.6 $ 1.1    
Restricted Stock Performance Plan [Member] | Award Opportunity 2013-2014 [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]        
Nonvested restricted shares granted (in shares)     159,940  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]        
Compensation expense   $ 3.1 $ 2.9