Debt (Credit Facility) (Narrative) (Details) (USD $)	12 Months Ended	0 Months Ended		12 Months Ended									0 Months Ended		12 Months Ended							0 Months Ended						12 Months Ended	0 Months Ended		0 Months Ended	12 Months Ended									0 Months Ended
	Dec. 31, 2013	Dec. 31, 2013 Line of Credit [Member]	Dec. 31, 2012 Line of Credit [Member]	Dec. 31, 2013 Line of Credit [Member] Federal Funds Rate [Member] Base Rate [Member]	Dec. 31, 2013 Line of Credit [Member] Eurocurrency [Member] Base Rate [Member]	Dec. 31, 2012 Line of Credit [Member] Letter of Credit [Member]	Dec. 31, 2012 Line of Credit [Member] Letter of Credit [Member] Maximum [Member]	Dec. 31, 2012 Line of Credit [Member] Letter of Credit [Member] Minimum [Member]	Dec. 31, 2013 Line of Credit [Member] Revolving Credit Facility [Member] Weighted Average [Member]	Dec. 31, 2012 Line of Credit [Member] Revolving Credit Facility [Member] Weighted Average [Member]	Dec. 31, 2013 Line of Credit [Member] 2011 Credit Facility [Member]	Dec. 31, 2012 Line of Credit [Member] 2011 Credit Facility [Member]	Dec. 31, 2013 Line of Credit [Member] 2011 Credit Facility [Member] Maximum [Member]	Dec. 31, 2013 Line of Credit [Member] 2011 Credit Facility [Member] Minimum [Member]	Dec. 31, 2013 Line of Credit [Member] 2011 Credit Facility [Member] Minimum [Member]	Dec. 31, 2012 Line of Credit [Member] 2011 Credit Facility [Member] Letter of Credit [Member]	Dec. 31, 2013 Line of Credit [Member] 2011 Credit Facility [Member] Letter of Credit [Member] Maximum [Member]	Dec. 31, 2013 Line of Credit [Member] 2011 Credit Facility [Member] Financial Standby Letter of Credit [Member] Maximum [Member]	Dec. 31, 2013 Line of Credit [Member] 2011 Credit Facility [Member] Financial Standby Letter of Credit [Member] Minimum [Member]	Dec. 31, 2013 Line of Credit [Member] 2011 Credit Facility [Member] Canada, Dollars Letter of Credit [Member]	Dec. 31, 2012 Line of Credit [Member] 2011 Credit Facility [Member] Revolving Credit Facility [Member]	Dec. 31, 2013 Line of Credit [Member] 2011 Credit Facility [Member] Revolving Credit Facility [Member] Maximum [Member] Base Rate [Member]	Dec. 31, 2013 Line of Credit [Member] 2011 Credit Facility [Member] Revolving Credit Facility [Member] Maximum [Member] Eurocurrency [Member]	Dec. 31, 2013 Line of Credit [Member] 2011 Credit Facility [Member] Revolving Credit Facility [Member] Minimum [Member] Base Rate [Member]	Dec. 31, 2013 Line of Credit [Member] 2011 Credit Facility [Member] Revolving Credit Facility [Member] Minimum [Member] Eurocurrency [Member]	Dec. 31, 2013 Line of Credit [Member] 2011 Credit Facility [Member] Financial Standby Letter of Credit [Member] Letter of Credit [Member] Maximum [Member]	Dec. 31, 2013 Line of Credit [Member] 2011 Credit Facility [Member] Financial Standby Letter of Credit [Member] Letter of Credit [Member] Minimum [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Maximum [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Maximum [Member] Permitted Acquisition [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Minimum [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Minimum [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Minimum [Member] Permitted Acquisition [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Letter of Credit [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Letter of Credit [Member] Maximum [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Letter of Credit [Member] Minimum [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Financial Standby Letter of Credit [Member] Maximum [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Financial Standby Letter of Credit [Member] Minimum [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Canada, Dollars Letter of Credit [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Revolving Credit Facility [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Revolving Credit Facility [Member] Maximum [Member] Base Rate [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Revolving Credit Facility [Member] Maximum [Member] Eurocurrency [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Revolving Credit Facility [Member] Minimum [Member] Base Rate [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Revolving Credit Facility [Member] Minimum [Member] Eurocurrency [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Revolving Credit Facility [Member] Canada, Dollars	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Financial Standby Letter of Credit [Member] Letter of Credit [Member] Maximum [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Financial Standby Letter of Credit [Member] Letter of Credit [Member] Minimum [Member]	Dec. 31, 2013 Loans Payable [Member] 2013 Credit Facility [Member] Maximum [Member]
Debt Instrument [Line Items]
Line of credit facility, expiration date																												Oct. 29, 2018
Line of credit facility, maximum borrowing capacity											$ 600,000,000																	$ 750,000,000
Line of credit, revolving loan sublimit																																													100,000,000
Line of credit facility, capacity available for specific purpose other than for trade purchases						229,200,000											350,000,000																	315,200,000	450,000,000													250,000,000
Line of credit, letter of credit sublimit																				25,000,000																			50,000,000
Swing loan													50,000,000																75,000,000
Deferred financing costs	9,600,000																											1,900,000
Line of credit facility, amount outstanding																					134,000,000																			53,000,000
Line of credit facility, interest rate							2.00%	1.00%	2.14%	3.95%							1.50%	1.25%	0.75%							2.50%	1.50%									0.75%	1.00%	0.50%								2.00%	1.00%
Letters of credit, outstanding amount																120,800,000																		134,800,000
Line of credit facility, remaining borrowing capacity												345,200,000																562,100,000
Debt instrument, basis spread, variable interest or fee				0.50%	1.00%																	1.50%	2.50%	0.50%	1.50%																1.00%	2.00%	0.00%	1.00%
Unused credit facility fee		0.30%	0.35%										0.45%	0.25%															0.40%		0.20%
Line of credit, percentage of consolidated EBITDA threshold, combined subsidiary guarantors															80.00%																	70.00%
Line of credit, percentage of consolidated EBITDA threshold, individual subsidiary guarantors															10.00%																	15.00%
Line of credit facility, leverage ratio																													3.5	3.75			3.5
Line of credit facility, interest coverage ratio																															3.0	3.0
Line of credit facility, permitted acquisitions amount, adjusted ratio of indebtedness to net capital																																	$ 50,000,000