Supplemental Guarantor Financial Information - Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	$ 217,892	$ 270,275	$ 256,553
Additions to property and equipment	(144,140)	(125,882)	(142,349)
Acquisitions, net of cash acquired	(487,077)	(22,669)	(103,874)
Proceeds from sale of assets and businesses		9,348	36,661
Net cash used in investing activities	(631,217)	(139,203)	(209,562)
Proceeds from borrowings under revolving credit facility	1,081,689	235,368	452,670
Repayments of borrowings under revolving credit facility	(976,161)	(311,362)	(499,551)
Proceeds from borrowings of long-term debt	300,000
Debt issuance costs	(5,704)
Tax payments related to share-based compensation	(8,504)
Proceeds from exercises of stock options	104	673	1,107
Additional tax benefit related to share-based compensation		338	1,985
Repurchase of common shares		(3,959)	(4,731)
Net cash provided by (used in) financing activities	391,424	(78,942)	(48,520)
Effect of exchange rate changes on cash	(263)	(4,893)	(4,049)
Net (decrease) increase in cash and cash equivalents	(22,164)	47,237	(5,578)
Cash and cash equivalents as of beginning of period	73,534	26,297	31,875
Cash and cash equivalents as of end of period	51,370	73,534	26,297
Eliminations
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities			370
Additions to property and equipment			(370)
Net cash used in investing activities			(370)
Parent [Member] | Reportable Legal Entities [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	8,388	(1,106)
Tax payments related to share-based compensation	(8,504)
Proceeds from exercises of stock options	104	526
Additional tax benefit related to share-based compensation		681
Net cash provided by (used in) financing activities	(8,400)	1,207
Net (decrease) increase in cash and cash equivalents	(12)	101
Cash and cash equivalents as of beginning of period	101
Cash and cash equivalents as of end of period	89	101
Issuer | Reportable Legal Entities [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	20,200	60,033	67,436
Proceeds from borrowings under revolving credit facility	352,600	198,826	379,400
Repayments of borrowings under revolving credit facility	(372,800)	(255,727)	(446,085)
Intercompany financing		248
Repayments of intercompany notes payable			1,670
Proceeds from exercises of stock options		147	1,107
Additional tax benefit related to share-based compensation		(343)	1,985
Repurchase of common shares		(3,959)	(4,731)
Net cash provided by (used in) financing activities	(20,200)	(60,808)	(66,654)
Net (decrease) increase in cash and cash equivalents		(775)	782
Cash and cash equivalents as of beginning of period	7	782
Cash and cash equivalents as of end of period	7	7	782
Guarantors [Member] | Reportable Legal Entities [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	164,993	101,430	110,945
Additions to property and equipment	(83,357)	(77,124)	(93,248)
Acquisitions, net of cash acquired	(468,930)	(17,512)	(72,434)
Proceeds from sale of assets and businesses		9,348	36,661
Net cash used in investing activities	(552,287)	(85,288)	(129,021)
Proceeds from borrowings under revolving credit facility	604,138
Repayments of borrowings under revolving credit facility	(495,944)
Proceeds from borrowings of long-term debt	300,000
Debt issuance costs	(5,704)
Intercompany financing	(6,605)	(14,430)
Repayments of intercompany notes payable			24,523
Net cash provided by (used in) financing activities	395,885	(14,430)	24,523
Effect of exchange rate changes on cash	221	(917)
Net (decrease) increase in cash and cash equivalents	8,812	795	6,447
Cash and cash equivalents as of beginning of period	6,995	6,200	(247)
Cash and cash equivalents as of end of period	15,807	6,995	6,200
Non-Guarantors [Member] | Reportable Legal Entities [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	24,311	109,918	77,802
Additions to property and equipment	(60,783)	(48,758)	(48,731)
Acquisitions, net of cash acquired	(18,147)	(5,157)	(31,440)
Net cash used in investing activities	(78,930)	(53,915)	(80,171)
Proceeds from borrowings under revolving credit facility	124,951	36,542	73,270
Repayments of borrowings under revolving credit facility	(107,417)	(55,635)	(53,466)
Intercompany financing	6,605	14,182
Repayments of intercompany notes payable			(26,193)
Net cash provided by (used in) financing activities	24,139	(4,911)	(6,389)
Effect of exchange rate changes on cash	(484)	(3,976)	(4,049)
Net (decrease) increase in cash and cash equivalents	(30,964)	47,116	(12,807)
Cash and cash equivalents as of beginning of period	66,431	19,315	32,122
Cash and cash equivalents as of end of period	$ 35,467	$ 66,431	$ 19,315