Accounts Receivable, Accounts Payable and Accrued Liabilities (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts Receivable, Net [Abstract]
Trade accounts receivable, less doubtful accounts and allowances	$ 591,854	$ 553,780
Other receivables	23,247	18,655
Accounts receivable, net	615,101	572,435
Allowance for Doubtful Accounts Receivable	26,723	27,854
Movement in Valuation Allowances and Reserves [Roll Forward]
Accounts payable and accrued liabilities	352,356	285,321
Accrued compensation and related benefits	148,370	142,693
Total accounts payable and accrued liabilities	500,726	428,014
Allowance for doubtful accounts[Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Begining of Period	27,854	32,598	$ 33,834
Additions - Charged to Costs and Expenses	29,718	39,982	47,356
Deductions	(30,849)	(44,726)	(48,592)
Balance at End of Period	$ 26,723	$ 27,854	$ 32,598