Selected Consolidated Financial Statements of Parent, Guarantors, Canada Company and Non-Guarantors - Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Cash Flows from Operating Activities:
Cash Flows from Operating Activities—Continuing Operations	$ 117,067	$ 91,568
Cash Flows from Operating Activities—Discontinued Operations	0	0
Cash Flows from Operating Activities	117,067	91,568
Cash Flows from Investing Activities:
Capital expenditures (see Liquidity and Capital Resources section of Management's Discussion & Analysis of Financial Condition and Results of Operations)	(184,765)	(95,605)
Cash paid for acquisitions, net of cash acquired	(39,423)	(1,428,974)
Intercompany loans to subsidiaries	0	0
Payments to Acquire Customer Relationships, Customer Inducements and Contract Fulfillment Costs	(67,912)	(18,046)
Proceeds from sales of property and equipment and other, net	105	(19,387)
Payments to Acquire Interest in Joint Venture	(19,222)	0
Cash Flows from Investing Activities—Continuing Operations	(311,217)	(1,562,012)
Cash Flows from Investing Activities—Discontinued Operations	0	0
Cash Flows from Investing Activities	(311,217)	(1,562,012)
Cash Flows from Financing Activities:
Repayment of revolving credit facility, term loan facilities and other debt	(1,351,242)	(4,410,656)
Proceeds from revolving credit facility, term loan facilities and other debt	1,723,462	5,496,491
Borrowings under cash pools	0	0
Debt financing from (repayment to) and equity contribution from (distribution to) noncontrolling interests, net	(498)	(561)
Intercompany loans from parent	0	0
Parent cash dividends	(178,023)	(169,006)
Net (payments) proceeds associated with employee stock-based awards	(5,963)	(5,950)
Net proceeds associated with the Over-Allotment Option	0	76,192
Net proceeds associated with the At the Market (ATM) Program	0	8,716
Payment of debt financing and stock issuance costs	0	(9,974)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations	187,736	985,252
Cash Flows from Financing Activities—Discontinued Operations	0	0
Net Cash Provided by (Used in) Financing Activities	187,736	985,252
Effect of exchange rates on cash and cash equivalents	2,404	1,984
Increase (Decrease) in cash and cash equivalents	(4,010)	(483,208)
Cash and cash equivalents, including Restricted Cash, beginning of period	165,485	925,699
Cash and cash equivalents, including Restricted Cash, end of period	161,475	442,491
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	161,475		$ 165,485
Eliminations
Cash Flows from Operating Activities:
Cash Flows from Operating Activities—Continuing Operations	0	0
Cash Flows from Operating Activities—Discontinued Operations	0	0
Cash Flows from Operating Activities	0	0
Cash Flows from Investing Activities:
Capital expenditures (see Liquidity and Capital Resources section of Management's Discussion & Analysis of Financial Condition and Results of Operations)	0	0
Cash paid for acquisitions, net of cash acquired	0	0
Intercompany loans to subsidiaries	275,034	366,180
Payments to Acquire Customer Relationships, Customer Inducements and Contract Fulfillment Costs	0	0
Proceeds from sales of property and equipment and other, net	0	0
Payments to Acquire Interest in Joint Venture	0
Cash Flows from Investing Activities—Continuing Operations	(275,034)	(366,180)
Cash Flows from Investing Activities—Discontinued Operations	0	0
Cash Flows from Investing Activities	(275,034)	(366,180)
Cash Flows from Financing Activities:
Repayment of revolving credit facility, term loan facilities and other debt	0	0
Proceeds from revolving credit facility, term loan facilities and other debt	0	0
Borrowings under cash pools	(5,026)	63,679
Debt financing from (repayment to) and equity contribution from (distribution to) noncontrolling interests, net	0	0
Intercompany loans from parent	275,034	366,180
Parent cash dividends	0	0
Net (payments) proceeds associated with employee stock-based awards	0	0
Net proceeds associated with the Over-Allotment Option		0
Net proceeds associated with the At the Market (ATM) Program		0
Payment of debt financing and stock issuance costs		0
Net Cash Provided by (Used in) Financing Activities, Continuing Operations	270,008	429,859
Cash Flows from Financing Activities—Discontinued Operations		0
Net Cash Provided by (Used in) Financing Activities	270,008	429,859
Effect of exchange rates on cash and cash equivalents	0	0
Increase (Decrease) in cash and cash equivalents	(5,026)	63,679
Cash and cash equivalents, including Restricted Cash, beginning of period	(65,615)	(94,726)
Cash and cash equivalents, including Restricted Cash, end of period	(70,641)	(31,047)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	(70,641)		(65,615)
Parent | Reportable legal entities
Cash Flows from Operating Activities:
Cash Flows from Operating Activities—Continuing Operations	(68,310)	(66,516)
Cash Flows from Operating Activities—Discontinued Operations	0	0
Cash Flows from Operating Activities	(68,310)	(66,516)
Cash Flows from Investing Activities:
Capital expenditures (see Liquidity and Capital Resources section of Management's Discussion & Analysis of Financial Condition and Results of Operations)	0	0
Cash paid for acquisitions, net of cash acquired	0	0
Intercompany loans to subsidiaries	(252,175)	(157,737)
Payments to Acquire Customer Relationships, Customer Inducements and Contract Fulfillment Costs	0	0
Proceeds from sales of property and equipment and other, net	0	0
Payments to Acquire Interest in Joint Venture	0
Cash Flows from Investing Activities—Continuing Operations	252,175	157,737
Cash Flows from Investing Activities—Discontinued Operations	0	0
Cash Flows from Investing Activities	252,175	157,737
Cash Flows from Financing Activities:
Repayment of revolving credit facility, term loan facilities and other debt	0	0
Proceeds from revolving credit facility, term loan facilities and other debt	0	0
Borrowings under cash pools	0	0
Debt financing from (repayment to) and equity contribution from (distribution to) noncontrolling interests, net	0	0
Intercompany loans from parent	0	0
Parent cash dividends	(178,023)	(169,006)
Net (payments) proceeds associated with employee stock-based awards	(5,963)	(5,950)
Net proceeds associated with the Over-Allotment Option		76,192
Net proceeds associated with the At the Market (ATM) Program		8,716
Payment of debt financing and stock issuance costs		(412)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations	(183,986)	(90,460)
Cash Flows from Financing Activities—Discontinued Operations	0	0
Net Cash Provided by (Used in) Financing Activities	(183,986)	(90,460)
Effect of exchange rates on cash and cash equivalents	0	0
Increase (Decrease) in cash and cash equivalents	(121)	761
Cash and cash equivalents, including Restricted Cash, beginning of period	132	2,433
Cash and cash equivalents, including Restricted Cash, end of period	11	3,194
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	11		132
Guarantors | Reportable legal entities
Cash Flows from Operating Activities:
Cash Flows from Operating Activities—Continuing Operations	116,235	96,674
Cash Flows from Operating Activities—Discontinued Operations	0	0
Cash Flows from Operating Activities	116,235	96,674
Cash Flows from Investing Activities:
Capital expenditures (see Liquidity and Capital Resources section of Management's Discussion & Analysis of Financial Condition and Results of Operations)	(84,766)	(62,148)
Cash paid for acquisitions, net of cash acquired	(9,508)	(1,315,549)
Intercompany loans to subsidiaries	(22,859)	(208,443)
Payments to Acquire Customer Relationships, Customer Inducements and Contract Fulfillment Costs	(49,301)	(11,874)
Proceeds from sales of property and equipment and other, net	36	(19,466)
Payments to Acquire Interest in Joint Venture	(19,222)
Cash Flows from Investing Activities—Continuing Operations	(139,902)	(1,200,594)
Cash Flows from Investing Activities—Discontinued Operations	0	0
Cash Flows from Investing Activities	(139,902)	(1,200,594)
Cash Flows from Financing Activities:
Repayment of revolving credit facility, term loan facilities and other debt	(410,563)	(2,308,119)
Proceeds from revolving credit facility, term loan facilities and other debt	734,243	3,067,988
Borrowings under cash pools	(10,612)	(51,946)
Debt financing from (repayment to) and equity contribution from (distribution to) noncontrolling interests, net	0	0
Intercompany loans from parent	(228,937)	(154,184)
Parent cash dividends	0	0
Net (payments) proceeds associated with employee stock-based awards	0	0
Net proceeds associated with the Over-Allotment Option		0
Net proceeds associated with the At the Market (ATM) Program		0
Payment of debt financing and stock issuance costs		(9,075)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations	84,131	544,664
Cash Flows from Financing Activities—Discontinued Operations	0	0
Net Cash Provided by (Used in) Financing Activities	84,131	544,664
Effect of exchange rates on cash and cash equivalents	0	0
Increase (Decrease) in cash and cash equivalents	60,464	(559,256)
Cash and cash equivalents, including Restricted Cash, beginning of period	61,650	634,317
Cash and cash equivalents, including Restricted Cash, end of period	122,114	75,061
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	122,114		61,650
Non-Guarantors | Reportable legal entities
Cash Flows from Operating Activities:
Cash Flows from Operating Activities—Continuing Operations	69,142	61,410
Cash Flows from Operating Activities—Discontinued Operations	0	0
Cash Flows from Operating Activities	69,142	61,410
Cash Flows from Investing Activities:
Capital expenditures (see Liquidity and Capital Resources section of Management's Discussion & Analysis of Financial Condition and Results of Operations)	(99,999)	(33,457)
Cash paid for acquisitions, net of cash acquired	(29,915)	(113,425)
Intercompany loans to subsidiaries	0	0
Payments to Acquire Customer Relationships, Customer Inducements and Contract Fulfillment Costs	(18,611)	(6,172)
Proceeds from sales of property and equipment and other, net	69	79
Payments to Acquire Interest in Joint Venture	0
Cash Flows from Investing Activities—Continuing Operations	(148,456)	(152,975)
Cash Flows from Investing Activities—Discontinued Operations	0	0
Cash Flows from Investing Activities	(148,456)	(152,975)
Cash Flows from Financing Activities:
Repayment of revolving credit facility, term loan facilities and other debt	(940,679)	(2,102,537)
Proceeds from revolving credit facility, term loan facilities and other debt	989,219	2,428,503
Borrowings under cash pools	(15,638)	11,733
Debt financing from (repayment to) and equity contribution from (distribution to) noncontrolling interests, net	(498)	(561)
Intercompany loans from parent	(46,097)	(211,996)
Parent cash dividends	0	0
Net (payments) proceeds associated with employee stock-based awards	0	0
Net proceeds associated with the Over-Allotment Option		0
Net proceeds associated with the At the Market (ATM) Program		0
Payment of debt financing and stock issuance costs		(487)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations	17,583	101,189
Cash Flows from Financing Activities—Discontinued Operations		0
Net Cash Provided by (Used in) Financing Activities	17,583	101,189
Effect of exchange rates on cash and cash equivalents	2,404	1,984
Increase (Decrease) in cash and cash equivalents	(59,327)	11,608
Cash and cash equivalents, including Restricted Cash, beginning of period	169,318	383,675
Cash and cash equivalents, including Restricted Cash, end of period	109,991	$ 395,283
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 109,991		$ 169,318