Basis of Presentation - Additional Information (Detail) (USD $)	3 Months Ended									12 Months Ended			0 Months Ended
	Dec. 31, 2014 Product Manufacturers_Distributors	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2014 Location Customer Product Manufacturers_Distributors	Dec. 31, 2013	Dec. 31, 2012	Oct. 31, 2014
Basis Of Presentation [Line Items]
Net sales	$ 1,333,082,000	$ 1,419,947,000	$ 1,320,037,000	$ 1,254,139,000	$ 1,223,638,000	$ 1,336,676,000	$ 1,274,494,000	$ 1,250,485,000		$ 5,327,205,000	$ 5,085,293,000	$ 5,080,106,000
Number of items	160,000									160,000
Number of manufacturers	1,600									1,600
Number of distribution centers										77
Number of reseller customer										30,000
Business acquisition cash paid									90,000,000
Purchase Price									79,800,000			79,800,000
Write off of investment					1,200,000
O.K.I. Supply Co. [Member]
Basis Of Presentation [Line Items]
Amount payable related to acquisition	4,500,000									4,500,000
Contribution to the Company's net financial sales										20,500,000
Pro forma net sales												5,200,000,000
Pro forma net income												112,600,000
CPO Commerce, Inc [Member]
Basis Of Presentation [Line Items]
Business acquisition cash paid										37,400,000
Amount payable related to acquisition	51,000									51,000
Business acquisition, fair value of contingent consideration	5,100,000									5,100,000
Business acquisition contingent consideration payments, range minimum	0									0
Business acquisition contingent consideration payments, range maximum	10,000,000									10,000,000
Stock acquisition, percentage acquired	100.00%									100.00%
MEDCO [Member]
Basis Of Presentation [Line Items]
Business acquisition cash paid													150,000,000
Amount payable related to acquisition	52,000									52,000			6,000,000
Contribution to the Company's net financial sales										36,300,000
Pro forma net sales										5,500,000,000	5,300,000,000	5,300,000,000
Pro forma net income										125,000,000	129,000,000	119,200,000
Business acquisition, fair value of contingent consideration													4,800,000
Business acquisition contingent consideration payments, range minimum													0
Business acquisition contingent consideration payments, range maximum													$ 10,000,000
Business acquisition acquired entity indemnification payment period													18 months