New Accounting Standards Adjustment for new accounting pronouncement (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement:
Net sales	$ 1,148,423	$ 1,135,027	$ 989,447	$ 913,600	$ 1,021,613	$ 1,086,014	$ 917,326	$ 868,682	$ 4,186,497	$ 3,893,635	$ 2,884,603
Cost of sales									3,429,224	3,198,158	2,405,338
Net income	$ 101,943	$ 55,630	$ 116,459	$ (9,144)	$ 101,202	$ 61,141	$ 5,366	$ (405)	$ 264,888	$ 167,304	$ 53,893
Basic (in dollars per share)	$ 0.42	$ 0.23	$ 0.48	$ (0.04)	$ 0.42	$ 0.25	$ 0.02	$ 0.00	$ 1.09	$ 0.69	$ 0.22
Diluted (in dollars per share)	$ 0.42	$ 0.23	$ 0.48	$ (0.04)	$ 0.42	$ 0.25	$ 0.02	$ 0.00	$ 1.09	$ 0.69	$ 0.22
Balance Sheet:
Accounts receivable, net	$ 692,287				$ 563,107				$ 692,287	$ 563,107
Inventories	326,492				267,990				326,492	267,990
Accrued expenses	374,598				338,669				374,598	338,669
(Accumulated deficit) retained earnings	(42,851)				$ (303,557)				(42,851)	(303,557)
New Revenue Standard Adjustment (Estimate) | Accounting Standards Update 2014-09
Income Statement:
Net sales									24,000	36,000
Cost of sales									17,000	21,000
Net income									$ 5,000	$ 11,000
Basic (in dollars per share)									$ 0.02	$ 0.05
Diluted (in dollars per share)									$ 0.02	$ 0.04
Balance Sheet:
Accounts receivable, net	106,000								$ 106,000
Inventories	(113,000)								(113,000)
Accrued expenses	(48,000)								(48,000)
(Accumulated deficit) retained earnings	31,000								31,000
As Adjusted (Estimate) | Accounting Standards Update 2014-09
Income Statement:
Net sales									4,210,497	$ 3,929,635
Cost of sales									3,446,224	3,219,158
Net income									$ 269,888	$ 178,304
Basic (in dollars per share)									$ 1.11	$ 0.74
Diluted (in dollars per share)									$ 1.11	$ 0.73
Balance Sheet:
Accounts receivable, net	798,287								$ 798,287
Inventories	213,492								213,492
Accrued expenses	326,598								326,598
(Accumulated deficit) retained earnings	$ (11,851)								$ (11,851)