Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts Receivable, Current	$ 2,783	$ 2,322
Accumulated depreciation	443,872	393,635
Accumulated amortization	$ 45,684	$ 39,018
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0
Preferred Stock, Shares Authorized	4,000	0
Preferred Stock, Shares Issued	0	0
Accounts Payable	$ 326,810	$ 367,307
Accrued Liabilities	113,783	81,104
Other Liabilities, Current	$ 1,920	$ 2,839
Common stock, $0.01 par value	$ 0.01	$ 0.01
Common stock shares authorized	100,000	100,000
Common stock shares issued	67,285	67,079
Treasury Stock, Common, Shares	1,013	980