Computation of Net Earnings per Share (Tables)
 3 Months Ended
Mar. 31, 2018
Earnings Per Share [Abstract]  
Computation of Basic and Diluted Net Earnings Per Common Share
The following table illustrates our computations of basic and diluted net earnings per common share ($ in thousands, except per
share figures):
 
Three months ended
 
March 31,
 
2018
 
2017
Net earnings
$
20,083

 
$
10,510

Average basic shares outstanding
10,915

 
10,998

Basic net earnings per share
$
1.84

 
$
0.96

 
 
 
 
Average basic shares outstanding
10,915

 
10,998

Restricted stock not vested
8

 
33

Dilutive effect of Performance Share Plan
86

 
96

Average diluted shares outstanding
11,009

 
11,127

Diluted net earnings per share
$
1.82

 
$
0.94