Quarterly report pursuant to Section 13 or 15(d)

Revenue - Cumulative Effect of Changes (Details)

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Revenue - Cumulative Effect of Changes (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Jan. 01, 2018
Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]      
Accounts Receivable, Net of Allowance for Doubtful Accounts $ 169,496 $ 136,638 $ 132,633
Inventories 159,479 142,239 150,196
Accrued Income Taxes   1,289  
Contract Liabilities 25,429 11,431 19,607
Deferred Income Taxes   5,049  
Retained Earnings   328,459  
Calculated under Revenue Guidance in Effect before Topic 606      
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]      
Accounts Receivable, Net of Allowance for Doubtful Accounts 163,166   132,633
Inventories 165,969   150,196
Accrued Income Taxes     261
Contract Liabilities 29,934   19,607
Deferred Income Taxes     5,121
Retained Earnings     $ 325,191
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09      
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]      
Accounts Receivable, Net of Allowance for Doubtful Accounts 6,330 4,005  
Inventories (6,490) (7,957)  
Accrued Income Taxes   1,028  
Contract Liabilities $ (4,505) (8,176)  
Deferred Income Taxes   (72)  
Retained Earnings   $ 3,268