Business Segment Information - Reconciliation of Operating Profit (Loss) from Segments to Consolidated (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Gross profit	$ 144,491	$ 114,530	$ 281,143	$ 214,226
Selling, general and administrative expenses	70,769	49,501	193,337	162,726
Acquisition and integration expenses	9,334	0	44,030	0
Gain on sales of property and equipment	(3,018)	(1,753)	(5,066)	(2,830)
Total other income	(383)	(2,522)	(1,869)	(2,987)
Income before provision for income taxes	67,789	69,304	50,711	57,317
Operating Segments [Member]
Segment Reporting Information [Line Items]
Gross profit	$ 144,491	$ 114,530	$ 281,143	$ 214,226