Summary of Significant Accounting Policies Cash Flow Accounting Guidance Recast (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Cash Provided by (Used in) Operating Activities	$ 211,458	$ 188,113
Capital expenditures	(46,241)	(40,150)
Acquisitions, net of cash acquired	(33,934)	(33,212)
Proceeds from divestitures and sales of property and equipment	6,452	20,235
Payments on Company-owned life insurance policies	(9,246)	(2,827)
Proceeds from Company-owned life insurance policies	2,810	906
Net cash used in investing activities	(80,089)	(55,048)
Net Cash Provided by (Used in) Financing Activities	(243,505)	(89,570)
Effect of foreign currency on cash, cash equivalents, and restricted cash	(1,145)	784
Net (decrease) increase in cash, cash equivalents, and restricted cash		44,279
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	227,320	255,785	$ 340,601	$ 211,506
Cash and cash equivalents	$ 219,507	255,785	$ 330,039
Adjustments for New Accounting Pronouncement [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Cash Provided by (Used in) Operating Activities		(270)
Capital expenditures		0
Acquisitions, net of cash acquired		(13,885)
Proceeds from divestitures and sales of property and equipment		17,087
Payments on Company-owned life insurance policies		(2,827)
Proceeds from Company-owned life insurance policies		906
Net cash used in investing activities		1,281
Net Cash Provided by (Used in) Financing Activities		0
Effect of foreign currency on cash, cash equivalents, and restricted cash		0
Net (decrease) increase in cash, cash equivalents, and restricted cash		1,011
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents				16,520
Cash and cash equivalents		17,531
Previous Accounting Guidance [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Cash Provided by (Used in) Operating Activities		188,383
Capital expenditures		(40,150)
Acquisitions, net of cash acquired		(19,327)
Proceeds from divestitures and sales of property and equipment		3,148
Payments on Company-owned life insurance policies		0
Proceeds from Company-owned life insurance policies		0
Net cash used in investing activities		(56,329)
Net Cash Provided by (Used in) Financing Activities		(89,570)
Effect of foreign currency on cash, cash equivalents, and restricted cash		784
Net (decrease) increase in cash, cash equivalents, and restricted cash		43,268
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents				$ 194,986
Cash and cash equivalents		$ 238,254