Condensed Consolidating Statements of Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Revenue	$ 1,316,689		$ 1,298,094		$ 1,251,748		$ 1,195,997		$ 1,067,915		$ 1,016,707		$ 1,006,531		$ 1,031,777		$ 5,062,528	$ 4,122,930	$ 3,269,862
Cost of goods sold																	2,987,126	2,398,790	1,877,869
Gross margin	545,673		517,907		509,873		501,949		445,121	[1]	409,705	[1]	421,931	[1]	447,383	[1]	2,075,402	1,724,140	1,391,993
Facility and warehouse expenses																	425,081	347,917	293,423
Distribution expenses																	431,947	375,835	287,626
Selling, general and administrative expenses																	597,052	495,591	391,942
Restructuring and acquisition related expenses																	10,173	2,751	7,590
Depreciation and amortization																	80,969	64,093	49,929
Operating income	133,819		123,395		131,378		141,588		104,344	[1]	91,434	[1]	108,567	[1]	133,608	[1]	530,180	437,953	361,483
Other expense (income):
Interest expense																	51,184	31,429	24,307
Intercompany interest (income) expense, net																	0	0	0
Loss on debt extinguishment																	2,795	0	5,345
Change in fair value of contingent consideration liabilities	(800)		(700)		(200)		(800)		200		(1,900)		(1,200)		1,300		(2,504)	(1,643)	1,408
Interest and other income, net																	(2,130)	(4,286)	(2,532)
Total other expense, net																	54,353	28,786	25,712
Income before provision for income taxes																	475,827	409,167	335,771
Provision for income taxes																	164,204	147,942	125,507
Equity in earnings of subsidiaries																	0	0	0
Net income	77,864	[2]	73,445	[2]	75,722	[2]	84,592	[2]	62,188	[2]	54,048	[2]	63,998	[2]	80,991	[2]	311,623	261,225	210,264
Parent Company
Condensed Financial Statements, Captions [Line Items]
Revenue																	0	0	0
Cost of goods sold																	0	0	0
Gross margin																	0	0	0
Facility and warehouse expenses																	0	0	0
Distribution expenses																	0	0	0
Selling, general and administrative expenses																	26,778	21,098	22,680
Restructuring and acquisition related expenses																	0	0	0
Depreciation and amortization																	250	296	239
Operating income																	(27,028)	(21,394)	(22,919)
Other expense (income):
Interest expense																	42,442	24,272	21,839
Intercompany interest (income) expense, net																	(45,459)	(37,491)	(36,018)
Loss on debt extinguishment																	2,795		5,345
Change in fair value of contingent consideration liabilities																	0	0	2,000
Interest and other income, net																	252	(43)	(332)
Total other expense, net																	30	(13,262)	(11,166)
Income before provision for income taxes																	(27,058)	(8,132)	(11,753)
Provision for income taxes																	(7,193)	(3,287)	(6,034)
Equity in earnings of subsidiaries																	331,488	266,070	215,983
Net income																	311,623	261,225	210,264
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Revenue																	3,576,269	3,236,507	2,975,275
Cost of goods sold																	2,100,804	1,886,098	1,721,419
Gross margin																	1,475,465	1,350,409	1,253,856
Facility and warehouse expenses																	323,042	287,036	261,260
Distribution expenses																	297,908	281,011	257,395
Selling, general and administrative expenses																	377,481	346,596	321,403
Restructuring and acquisition related expenses																	1,406	1,812	3,438
Depreciation and amortization																	55,802	49,782	44,724
Operating income																	419,826	384,172	365,636
Other expense (income):
Interest expense																	640	308	99
Intercompany interest (income) expense, net																	21,978	27,377	31,036
Loss on debt extinguishment																	0		0
Change in fair value of contingent consideration liabilities																	744	1,943	(11)
Interest and other income, net																	(2,858)	(3,638)	(1,979)
Total other expense, net																	19,016	22,104	29,167
Income before provision for income taxes																	400,810	362,068	336,469
Provision for income taxes																	151,369	140,150	128,930
Equity in earnings of subsidiaries																	22,050	12,481	3,036
Net income																	271,491	234,399	210,575
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Revenue																	1,598,832	976,710	370,912
Cost of goods sold																	998,895	602,979	232,775
Gross margin																	599,937	373,731	138,137
Facility and warehouse expenses																	102,039	60,881	32,163
Distribution expenses																	134,039	94,824	30,231
Selling, general and administrative expenses																	192,793	127,897	47,859
Restructuring and acquisition related expenses																	8,767	939	4,152
Depreciation and amortization																	24,917	14,015	4,966
Operating income																	137,382	75,175	18,766
Other expense (income):
Interest expense																	8,102	6,849	2,369
Intercompany interest (income) expense, net																	23,481	10,114	4,982
Loss on debt extinguishment																	0		0
Change in fair value of contingent consideration liabilities																	(3,248)	(3,586)	(581)
Interest and other income, net																	476	(605)	(221)
Total other expense, net																	35,307	19,944	7,711
Income before provision for income taxes																	102,075	55,231	11,055
Provision for income taxes																	20,028	11,079	2,611
Equity in earnings of subsidiaries																	0	0	0
Net income																	82,047	44,152	8,444
Consolidation, Eliminations
Condensed Financial Statements, Captions [Line Items]
Revenue																	(112,573)	(90,287)	(76,325)
Cost of goods sold																	(112,573)	(90,287)	(76,325)
Gross margin																	0	0	0
Facility and warehouse expenses																	0	0	0
Distribution expenses																	0	0	0
Selling, general and administrative expenses																	0	0	0
Restructuring and acquisition related expenses																	0	0	0
Depreciation and amortization																	0	0	0
Operating income																	0	0	0
Other expense (income):
Interest expense																	0	0	0
Intercompany interest (income) expense, net																	0	0	0
Loss on debt extinguishment																	0		0
Change in fair value of contingent consideration liabilities																	0	0	0
Interest and other income, net																	0	0	0
Total other expense, net																	0	0	0
Income before provision for income taxes																	0	0	0
Provision for income taxes																	0	0	0
Equity in earnings of subsidiaries																	(353,538)	(278,551)	(219,019)
Net income																	$ (353,538)	$ (278,551)	$ (219,019)

[1] Gross margin and operating income during the quarters ended March 31, 2012, June 30, 2012, September 30, 2012 and December 31, 2012 include gains of $8.3 million, $8.4 million, $0.5 million and $0.7 million, respectively, resulting from lawsuit settlements with certain of our aftermarket product suppliers as discussed in Note 7, "Commitments and Contingencies."

[2] Net income during the quarters ended March 31, 2012 and December 31, 2012 include gains for changes in fair value of our contingent consideration liabilities of $1.3 million and $0.2 million, respectively, while the quarters ended June 30, 2012 and September 30, 2012 include losses of $1.2 million and $1.9 million, respectively. The quarters ended March 31, 2013, June 30, 2013, September 30, 2013 and December 31, 2013 include losses for changes in fair value of our contingent consideration liabilities of $0.8 million, $0.2 million, $0.7 million and $0.8 million, respectively. See Note 6, "Fair Value Measurements," for further information on these changes in fair value of the contingent consideration obligations recorded in earnings during the periods.