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Valuation and Qualifying Accounts Valuation and Qualifying Accounts (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Employee severance accruals      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at beginning of year $ 1,141 $ 0 $ 1,517
Charged to costs and expenses 1,265 1,649 571
Deduction 1,569 508 2,088
Balance at end of year 837 1,141 0
Valuation allowance of the deferred tax asset      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at beginning of year 276 244 209
Charged to costs and expenses 0 32 35
Deduction 43 0 0
Balance at end of year 233 276 244
SEC Schedule, 12-09, Valuation Allowance, Current [Member]      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at beginning of year 769 835 746
Charged to costs and expenses 1,088 1,111 1,248
Deduction 1,008 1,177 1,159
Balance at end of year 849 769 835
SEC Schedule, 12-09, Valuation Allowance, Noncurrent [Member]      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at beginning of year 2,151 2,278 2,166
Charged to costs and expenses 532 730 950
Deduction 457 857 838
Balance at end of year $ 2,226 $ 2,151 $ 2,278