Basis of Presentation and Significant Accounting Policies - Allowance for doubtful accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Shipping, Handling and Transportation Costs	$ 26,370	$ 26,641	$ 33,598
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance, beginning of year	2,380	2,471	2,744
Add Provision charged to expense	37	678	184
Add Recoveries	32	26	105
Less Charges against allowance	(504)	(795)	(562)
Balance, end of year	$ 1,945	$ 2,380	$ 2,471