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Revenue Recognition Policies (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2018
Apr. 01, 2017
Dec. 31, 2017
Dec. 31, 2016
Distributor sales accruals [Line Items]        
Distributor sales accrual, Beginning Balance $ 36,680 $ 34,479 $ 34,479 $ 32,487
Distributor sales accrual, sales allowance 24,188 21,520 89,009 86,896
Distributor sales accrual, credits issued (28,450) (23,471) (87,403) (85,341)
Distributor sales accrual, foreign currency 288 (576) 595 437
Distributor sales accrual, Ending Balance $ 32,706 $ 31,952 $ 36,680 $ 34,479