Basis of Presentation and Significant Accounting Policies - Allowance for doubtful accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Shipping, Handling and Transportation Costs	$ 28,320	$ 35,471	$ 35,171
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance, beginning of year	3,375	3,463	3,529
Add Provision charged to expense	805	465	484
Add Recoveries	117	139	173
Less Charges against allowance	(857)	(692)	(723)
Balance, end of year	$ 3,440	$ 3,375	$ 3,463