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Organization, Business and Significant Accounting Policies (Details)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2020
USD ($)
$ / shares
Sep. 30, 2020
USD ($)
$ / shares
Jun. 30, 2020
USD ($)
$ / shares
Mar. 31, 2020
USD ($)
$ / shares
Dec. 31, 2019
USD ($)
$ / shares
Sep. 30, 2019
USD ($)
$ / shares
Jun. 30, 2019
USD ($)
$ / shares
Mar. 31, 2019
USD ($)
$ / shares
Dec. 31, 2020
USD ($)
segment
$ / shares
Dec. 31, 2019
USD ($)
$ / shares
Dec. 31, 2018
USD ($)
$ / shares
Jan. 01, 2020
USD ($)
Dec. 31, 2017
USD ($)
Organization Consolidation and Presentation of Financial Statements [Line Items]                          
Number of business segments | segment                 2        
Contract retention provision                 10.00%        
Revenue recognized, related to change orders and claims included as contract price adjustments                 $ 14,700 $ 35,900      
Increase (decrease) in operating income                 86,545 57,178 $ 50,312    
Increase (decrease) in net income $ 18,150 $ 17,292 $ 13,385 $ 9,932 $ 12,775 $ 10,355 $ 7,207 $ 7,353 $ 58,759 $ 37,690 $ 31,087    
Increase (decrease) in diluted earnings per common share (in dollars per share) | $ / shares $ 1.07 $ 1.02 $ 0.80 $ 0.59 $ 0.76 $ 0.62 $ 0.43 $ 0.44 $ 3.48 $ 2.26 $ 1.87    
Advertising cost                 $ 700 $ 800 $ 700    
Allowance for contract retainage $ 400       $ 100       $ 400 100      
Option to extend lease term (up to)                 5 years        
Option to terminate leases, period                 1 year        
Decrease in retained earnings 429,292       364,475       $ 429,292 364,475 324,464   $ 287,039
Allowance for contract assets 359       147       359 147   $ 400  
Retained Earnings                          
Organization Consolidation and Presentation of Financial Statements [Line Items]                          
Decrease in retained earnings 270,480       212,219       $ 270,480 212,219 $ 174,736   143,241
Cumulative Effect, Period of Adoption, Adjustment                          
Organization Consolidation and Presentation of Financial Statements [Line Items]                          
Decrease in retained earnings         (268)         (268)     695
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings                          
Organization Consolidation and Presentation of Financial Statements [Line Items]                          
Decrease in retained earnings         $ (268)         $ (268)   $ (300) $ 695
Revenue from Contract with Customer | Top Ten Customers | Customer Concentration Risk                          
Organization Consolidation and Presentation of Financial Statements [Line Items]                          
Concentration risk                 32.70% 30.80% 32.90%    
Labor employees covered by collective bargaining agreements | Labor Force Concentration Risk                          
Organization Consolidation and Presentation of Financial Statements [Line Items]                          
Concentration risk                 88.00%        
Contingencies Excluding Wildfire and Health Insurance                          
Organization Consolidation and Presentation of Financial Statements [Line Items]                          
Insurance coverage deductible 1,000               $ 1,000        
Wildfire                          
Organization Consolidation and Presentation of Financial Statements [Line Items]                          
Insurance coverage deductible 2,000               2,000        
Health Insurance                          
Organization Consolidation and Presentation of Financial Statements [Line Items]                          
Insurance coverage deductible $ 200               $ 200        
Minimum                          
Organization Consolidation and Presentation of Financial Statements [Line Items]                          
Remaining lease term                 1 year        
Maximum                          
Organization Consolidation and Presentation of Financial Statements [Line Items]                          
Remaining lease term                 6 years        
Contracts Accounted for under Percentage of Completion                          
Organization Consolidation and Presentation of Financial Statements [Line Items]                          
Increase (decrease) in consolidated gross margin                 (0.80%) (0.80%) (0.70%)    
Increase (decrease) in operating income                 $ (18,000) $ (11,700) $ (10,500)    
Increase (decrease) in net income                 $ (12,800) $ (7,500) $ (8,200)    
Increase (decrease) in diluted earnings per common share (in dollars per share) | $ / shares                 $ (0.76) $ (0.45) $ (0.49)