Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	3 Months Ended					9 Months Ended		12 Months Ended
	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 35,809	$ 34,366		$ 33,812	$ 47,336	$ 117,702	$ 128,372
Adjustments to reconcile net income to cash flows provided by operating activities:
Depreciation and amortization						55,882	49,739
Stock-based compensation expense						12,061	13,852
Other non-cash items						837	(959)
Changes in assets and liabilities, net of acquisitions of businesses:
Accounts receivable, net						(42,367)	(51,733)
Inventories, net						24,410	(16,475)
Prepaid expenses and other assets						15,119	(9,506)
Accounts payable, trade						8,437	(12,930)
Accrued expenses and other liabilities						17,461	7,232
Net cash flows provided by operating activities						209,542	107,592
Cash flows from investing activities:
Capital expenditures						(47,767)	(92,522)
Acquisitions of businesses, net of cash acquired						(53,923)	(156,701)
Proceeds from note receivable						0	2,000
Other investing activities						364	(875)
Net cash flows used in investing activities						(101,326)	(248,098)
Cash flows from financing activities:
Exercise of stock-based awards, net of shares tendered for payment of taxes						(7,194)	(14,114)
Proceeds from line of credit borrowings						404,228	928,601
Repayments under line of credit borrowings						(443,921)	(738,601)
Proceeds from other borrowings						0	4,509
Payment of dividends						(47,533)	(44,114)
Payment of contingent consideration related to acquisitions						(4)	(3,018)
Other financing activities						(401)	(556)
Net cash flows provided by (used in) financing activities						(94,825)	132,707
Effect of exchange rate changes on cash, cash equivalents, and restricted cash						(842)	0
Net decrease in cash and cash equivalents						12,549	(7,799)
Cash, cash equivalents, and restricted cash at beginning of period		$ 14,928	$ 18,250		$ 26,049	14,928	26,049	$ 26,049
Cash, cash equivalents, and restricted cash at end of period	$ 27,477		$ 14,928	$ 18,250		27,477	18,250	$ 14,928
Supplemental disclosure of cash flow information:
Cash paid during the period for interest						6,156	4,244
Cash paid during the period for income taxes, net of refunds						28,416	33,844
Purchase of property and equipment in accrued expenses						$ 588	$ 467