Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 47,527	$ 34,366	$ 47,224	$ 47,336	$ 81,893	$ 94,560
Adjustments to reconcile net income to cash flows provided by operating activities:
Depreciation and amortization					37,115	32,476
Stock-based compensation expense					7,848	9,762
Other non-cash items					705	(927)
Changes in assets and liabilities, net of acquisitions of businesses:
Accounts receivable, net					(22,345)	(52,236)
Inventories, net					39,944	(14,556)
Prepaid expenses and other assets					11,444	(5,743)
Accounts payable, trade					11,567	5,412
Accrued expenses and other liabilities					11,944	10,181
Net cash flows provided by operating activities					180,115	78,929
Cash flows from investing activities:
Capital expenditures					(35,786)	(54,539)
Acquisitions of businesses, net of cash acquired					(8,530)	(153,415)
Proceeds from note receivable					0	2,000
Other investing activities					251	(1,016)
Net cash flows used in investing activities					(44,065)	(206,970)
Cash flows from financing activities:
Exercise of stock-based awards, net of shares tendered for payment of taxes					(7,144)	(14,114)
Proceeds from line of credit borrowings					305,288	631,148
Repayments under line of credit borrowings					(354,981)	(469,148)
Proceeds from other borrowings					0	4,509
Payment of dividends					(31,266)	(28,985)
Payment of contingent consideration related to acquisitions					(4)	(3,011)
Other financing activities					(393)	(556)
Net cash flows provided by (used in) financing activities					(88,500)	119,843
Effect of exchange rate changes on cash, cash equivalents, and restricted cash					(1,818)	0
Net decrease in cash and cash equivalents					45,732	(8,198)
Cash, cash equivalents, and restricted cash at beginning of period		$ 14,928		$ 26,049	14,928	26,049	$ 26,049
Cash, cash equivalents, and restricted cash at end of period	$ 60,660		$ 17,851		60,660	17,851	$ 14,928
Supplemental disclosure of cash flow information:
Cash paid during the period for interest					3,948	2,582
Cash paid during the period for income taxes, net of refunds					13,890	24,907
Purchase of property and equipment in accrued expenses					$ 298	$ 664