Sum of the carrying values as of the balance sheet date of obligations incurred through that date and due within one year (or the operating cycle, if longer), including liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received, taxes, interest, rent and utilities, accrued salaries and bonuses, payroll taxes and fringe benefits.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Effects of ASC 606 Adoption on the Consolidated Income Statement and Balance Sheet (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Statement of Income Items
Revenues	$ 794,977	$ 919,762
Cost of service	252,386	455,936
Selling, general and administrative expenses	386,421	358,856
Provision for income taxes	(24,673)	$ (12,321)
Assets:
Accounts receivable, net of allowances for doubtful accounts	288,101			$ 301,887
Prepaid expenses and other current assets	213,841			206,545
Deferred income taxes	11,420			13,146
Other noncurrent assets	323,019			207,297
Liabilities:
Accounts payable and accrued liabilities	1,039,379			1,039,607
Deferred income taxes	452,470			436,879
Other noncurrent liabilities	225,267			220,961
Shareholders' Equity:
Retained earnings	1,738,545			1,597,897
Accumulated other comprehensive loss	(176,961)			$ (183,144)
Without Effects of New Accounting Standard
Statement of Income Items
Revenues	1,045,570
Cost of service	489,305
Selling, general and administrative expenses	410,242
Provision for income taxes	(22,384)
Assets:
Accounts receivable, net of allowances for doubtful accounts	286,665
Prepaid expenses and other current assets	214,326
Deferred income taxes	12,523
Other noncurrent assets	249,772
Liabilities:
Accounts payable and accrued liabilities	1,039,223
Deferred income taxes	436,735
Other noncurrent liabilities	224,802
Shareholders' Equity:
Retained earnings	1,679,811
Accumulated other comprehensive loss	(174,966)
Accounting Standards Update 2014-09 \| Effects of New Accounting Standard
Statement of Income Items
Revenues	250,593
Cost of service	236,919
Selling, general and administrative expenses	23,821
Provision for income taxes	2,289
Assets:
Accounts receivable, net of allowances for doubtful accounts	(1,436)
Prepaid expenses and other current assets	485
Deferred income taxes	1,103
Other noncurrent assets	(73,247)		$ 64,600
Liabilities:
Accounts payable and accrued liabilities	(156)
Deferred income taxes	(15,735)		15,600
Other noncurrent liabilities	(465)
Shareholders' Equity:
Retained earnings	(58,734)		$ 51,000
Accumulated other comprehensive loss	$ 1,995