Long-Term Debt (Narrative) (Details) - USD ($)
 3 Months Ended 9 Months Ended
May 31, 2018
May 07, 2018
Nov. 30, 2016
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Mar. 19, 2014
Debt Covenant To Actual Ratios [Line Items]                  
Repayments of Long-term Lines of Credit           $ 188,000,000 $ 67,300,000    
Revolving credit facility present accordion provisions       $ 75,000,000   75,000,000      
Debt Issuance Costs, Gross       $ 900,000   $ 900,000      
Debt Covenant, Percentage Operations       50.00%   50.00%      
Carrying value of the liability component       $ 318,956,000   $ 318,956,000   $ 0  
Deferred payments     $ 2,000,000            
Accumulated Amortization, Debt Issuance Costs       4,518,000   4,518,000   4,442,000  
Amortization of Debt Issuance Costs           420,000 614,000    
Net loss on early extinguishment of debt       $ 0 $ 0 (936,000) 0    
Write off of Deferred Debt Issuance Cost $ 700,000                
Interest Expense, Debt           $ 7,200,000      
Term Number Two [Member]                  
Debt Covenant To Actual Ratios [Line Items]                  
Ratio of indebtedness to net capital (in Ratio) (below at March 31, 2015)       5.5   5.5      
Ratio Minimum Per Covenant [Member]                  
Debt Covenant To Actual Ratios [Line Items]                  
Ratio of earnings to fixed cost obligations (in Ratio)       1.2   1.2      
Ratio Actual [Member]                  
Debt Covenant To Actual Ratios [Line Items]                  
Ratio of indebtedness to net capital (in Ratio) (below at March 31, 2015)       4.86   4.86      
Ratio of earnings to fixed cost obligations (in Ratio)       1.95   1.95      
Revolving Credit Facility [Member]                  
Debt Covenant To Actual Ratios [Line Items]                  
Revolving credit facility, maximum borrowing capacity       $ 200,000,000   $ 200,000,000      
Write off of Deferred Debt Issuance Cost 900,000     1,600,000   1,600,000      
Term Loan [Member]                  
Debt Covenant To Actual Ratios [Line Items]                  
Revolving credit facility, maximum borrowing capacity       150,000,000   150,000,000      
Term Loan [Member]                  
Debt Covenant To Actual Ratios [Line Items]                  
Revolving credit facility, maximum borrowing capacity       148,019,435   148,019,435      
Convertible Subordinated Notes [Member]                  
Debt Covenant To Actual Ratios [Line Items]                  
Gain (Loss) On Repurchase Of Convertible Junior Subordinated Debentures   $ 1,200,000              
Component of Convertible Debt, Transaction Expense, Early Extinguishment   500,000              
Carrying value of the liability component       25,697,000   25,697,000   124,441,000  
Accumulated Amortization, Debt Issuance Costs       455,000   455,000   $ 1,877,000  
Amortization of Debt Issuance Costs       27,000 130,000 200,000 400,000    
Write off of Deferred Debt Issuance Cost   $ 1,300,000   $ 700,000   $ 700,000      
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed   80.00%              
Stated interest rate percentage       2.75%   2.75%     2.75%
Interest Expense, Debt       $ 200,000 1,000,000 $ 1,700,000 3,000,000    
Senior Notes [Member]                  
Debt Covenant To Actual Ratios [Line Items]                  
Principal amount       325,000,000   325,000,000      
Repayments of Long-term Lines of Credit $ 291,400,000                
Debt Issuance Costs, Gross       $ 1,400,000   $ 1,400,000      
Weighted average interest rate       6.87%   6.69%      
Accumulated Amortization, Debt Issuance Costs       $ 11,000   $ 11,000      
Amortization of Debt Issuance Costs       $ 33,000   $ 44,000      
Stated interest rate percentage       6.625%   6.625%      
Interest Expense, Debt       $ 5,400,000   $ 7,200,000      
Credit Agreement [Member]                  
Debt Covenant To Actual Ratios [Line Items]                  
Amortization of Debt Issuance Costs         100,000        
Credit Agreement [Member] | Revolving Credit Facility [Member]                  
Debt Covenant To Actual Ratios [Line Items]                  
Amount drawn under term loan facility       0   $ 0      
Credit Agreement [Member] | Revolving Credit Facility [Member] | QTD [Member]                  
Debt Covenant To Actual Ratios [Line Items]                  
Weighted average interest rate           4.00%      
Credit Agreement [Member] | Term Loan [Member]                  
Debt Covenant To Actual Ratios [Line Items]                  
Debt Instrument, Basis Spread on Variable Rate           2.125%      
Prime Rate Option [Member] | Line of Credit [Member]                  
Debt Covenant To Actual Ratios [Line Items]                  
Debt Instrument, Basis Spread on Variable Rate           1.00%      
Libor Margin Option [Member] | Line of Credit [Member]                  
Debt Covenant To Actual Ratios [Line Items]                  
Debt Instrument, Basis Spread on Variable Rate           2.00%      
Series of Individually Immaterial Business Acquisitions [Member]                  
Debt Covenant To Actual Ratios [Line Items]                  
Interest Expense, Debt       $ 200,000 $ 300,000 $ 600,000 $ 700,000