Consolidated Statements Of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Cash flows - operating activities:
Net income including noncontrolling interests		$ 283,577		$ 227,193		$ 182,153
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		38,472		39,915		38,881
Amortization of identifiable intangible assets		42,443		48,594		40,908
Provision for doubtful accounts		2,123		7,264		6,194
Deferred income taxes		4,249		(53,358)		(8,108)
Gain on sale of property, plant and equipment		(517)		(1,846)		(330)
Excess tax benefits from share-based compensation		(1,646)		(1,616)		(2,546)
Equity income from unconsolidated entities		(347)		(864)		(1,569)
Non-cash expense for amortization of debt issuance costs		1,186		1,186		1,354
Non-cash expense from contingent consideration arrangements		186		317		0
Non-cash expense for impairment of goodwill and identifiable intangible assets		907		57,819		2,428
Non-cash share-based compensation expense		11,030		9,939		8,902
Non-cash income from changes in unrecognized tax benefits		(72)		(5,641)		(759)
Distributions from unconsolidated entities		3,110		5,506		1,247
Changes in operating assets and liabilities, excluding the effect of businesses acquired:
Increase in accounts receivable		(146,101)		(80,514)		(98,773)
(Increase) decrease in inventories		(3,915)		(4,936)		954
(Increase) decrease in contract assets		(30,935)		12,433		(7,851)
Increase in accounts payable		78,554		54,910		13,141
Increase in contract liabilities		20,726		24,695		57,244
(Decrease) increase in accrued payroll and benefits and other accrued expenses and liabilities		(24,715)		24,017		22,659
Changes in other assets and liabilities, net		(7,304)		1,036		6,243
Net cash provided by operating activities		271,011		366,049		262,372
Cash flows - investing activities:
Payments for acquisitions of businesses, net of cash acquired		(72,080)		(107,223)		(232,947)
Proceeds from sale of property, plant and equipment		1,237		4,014		2,023
Purchase of property, plant and equipment		(43,479)		(34,684)		(39,648)
Investments in and advances to unconsolidated entities		(3,484)		(675)		(99)
Distributions from unconsolidated entities		84		475		0
Net cash used in investing activities		(117,722)		(138,093)		(270,671)
Cash flows - financing activities:
Proceeds from revolving credit facility		0		0		220,000
Repayments of revolving credit facility		0		(100,000)		(95,000)
Borrowings from long-term debt		0		0		400,000
Repayments of long-term debt and debt issuance costs		(15,235)		(15,202)		(417,990)
Repayments of capital lease obligations		(1,501)		(1,445)		(1,384)
Dividends paid to stockholders		(18,640)		(18,971)		(19,454)
Repurchase of common stock		(216,244)		(93,166)		(94,221)
Proceeds from exercise of stock options		0		0		741
Taxes paid related to net share settlements of equity awards		(3,848)		(3,462)		(4,225)
Issuance of common stock under employee stock purchase plan		5,765		4,793		4,814
Payments for contingent consideration arrangements		(3,339)		(1,017)		0
Distributions to noncontrolling interests		0		0		(2,710)
Net cash used in financing activities		(253,042)		(228,470)		(9,429)
Effect of exchange rate changes on cash, cash equivalents and restricted cash		(3,421)		3,242		(6,675)
(Decrease) increase in cash, cash equivalents and restricted cash		(103,174)		2,728		(24,403)
Cash, cash equivalents and restricted cash at beginning of year (1)		469,388	[1]	466,660	[1]	491,063
Cash, cash equivalents and restricted cash at end of period (1)	[1]	$ 366,214		$ 469,388		$ 466,660

[1] Includes $2.3 million, $2.0 million, $2.0 million and $4.2 million of restricted cash classified as “Prepaid expenses and other” in the Consolidated Balance Sheet as of December 31, 2018, 2017, 2016 and 2015, respectively.