Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts Receivable, Current	$ 2,561	$ 2,322
Accumulated depreciation	416,406	393,635
Accumulated amortization	42,606	39,018
Accounts Payable	417,586	367,307
Accrued Liabilities	87,368	81,104
Other Liabilities, Current	$ 3,317	$ 2,839
Common stock, $0.01 par value	$ 0.01	$ 0.01
Common stock shares authorized	100,000	100,000
Common stock shares issued	67,244	67,079
Treasury Stock, Common, Shares	1,007	980