Guarantor and Nonguarantor Financial Statements - Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	$ 1,131,249	$ 894,411	$ 616,985
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(227,803)	(178,042)	(191,205)
Acquisition of businesses, including net assets acquired, intangibles and goodwill, net of cash acquired	(322,573)	(118,427)	(21,077)
Contributions to unconsolidated subsidiaries	(62,802)	(68,700)	(66,816)
Distributions from unconsolidated subsidiaries	61,709	63,664	46,775
Net proceeds from disposition of real estate held for investment	14,174		44,326
Purchase of equity securities	(21,402)	(15,584)	(15,506)
Proceeds from sale of equity securities	16,314	15,587	16,954
Purchase of available for sale debt securities	(23,360)	(19,280)	(22,155)
Proceeds from the sale of available for sale debt securities	5,792	15,790	18,097
Other investing activities, net	(733)	2,392	40,083
Net cash used in investing activities	(560,684)	(302,600)	(150,524)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from senior term loans	1,002,745	200,000
Repayment of senior term loans	(450,000)	(751,876)	(136,250)
Proceeds from revolving credit facility	3,258,000	1,521,000	2,909,000
Repayment of revolving credit facility	(3,258,000)	(1,521,000)	(2,909,000)
Repayment of 5.00% senior notes (including premium)	(820,000)
Proceeds from notes payable on real estate	7,599	4,333	25,001
Repayment of notes payable on real estate	(19,058)	(12,556)	(38,046)
Repayment of debt assumed in acquisition of FacilitySource	(26,295)
Repurchase of common stock	(161,034)
Acquisition of businesses (cash paid for acquisitions more than three months after purchase date)	(18,660)	(24,006)	(21,034)
Units repurchased for payment of taxes on equity awards	(29,386)	(29,549)	(27,426)
Non-controlling interest contributions	25,355	5,301	2,272
Non-controlling interest distributions	(13,413)	(8,715)	(19,133)
Payment of financing costs	(2,088)	(7,999)	(5,618)
Other financing activities, net	(2,365)	(2,675)	(443)
Net cash used in financing activities	(506,600)	(627,742)	(220,677)
Effect of currency exchange rate changes on cash and cash equivalents and restricted cash	(24,840)	29,338	(27,539)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS AND RESTRICTED CASH	39,125	(6,593)	218,245
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, AT BEGINNING OF PERIOD	824,819	831,412	613,167
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, AT END OF PERIOD	863,944	824,819	831,412
Cash paid during the period for:
Interest	104,165	117,164	125,800
Income taxes, net	375,849	356,997	294,848
Parent [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	105,850	89,341	84,393
CASH FLOWS FROM FINANCING ACTIVITIES:
Repurchase of common stock	(161,034)
Units repurchased for payment of taxes on equity awards	(29,386)	(29,549)	(27,426)
Decrease (increase) in intercompany receivables, net	84,213	(60,271)	(57,880)
Other financing activities, net	357	479	915
Net cash used in financing activities	(105,850)	(89,341)	(84,391)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS AND RESTRICTED CASH			2
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, AT BEGINNING OF PERIOD	7	7	5
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, AT END OF PERIOD	7	7	7
CBRE Services [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	21,834	37,990	(23,643)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from senior term loans	550,000	200,000
Repayment of senior term loans	(450,000)	(751,876)	(136,250)
Proceeds from revolving credit facility	3,258,000	1,521,000	2,909,000
Repayment of revolving credit facility	(3,258,000)	(1,521,000)	(2,909,000)
Repayment of 5.00% senior notes (including premium)	(820,000)
Payment of financing costs	(212)	(7,978)	(5,459)
Decrease (increase) in intercompany receivables, net	716,837	520,579	173,762
Net cash used in financing activities	(3,375)	(39,275)	32,053
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS AND RESTRICTED CASH	18,459	(1,285)	8,410
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, AT BEGINNING OF PERIOD	15,604	16,889	8,479
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, AT END OF PERIOD	34,063	15,604	16,889
Cash paid during the period for:
Interest	102,491	117,072	122,605
Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	429,540	424,787	296,501
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(140,670)	(121,347)	(115,049)
Acquisition of businesses, including net assets acquired, intangibles and goodwill, net of cash acquired	(305,315)	(87,248)	(2,191)
Contributions to unconsolidated subsidiaries	(51,046)	(63,119)	(47,192)
Distributions from unconsolidated subsidiaries	57,269	52,896	39,340
Purchase of equity securities	(21,402)	(15,584)	(15,506)
Proceeds from sale of equity securities	16,314	15,587	16,954
Purchase of available for sale debt securities	(23,360)	(19,280)	(22,155)
Proceeds from the sale of available for sale debt securities	5,792	15,790	18,097
Other investing activities, net	2,793	1,968	19,178
Net cash used in investing activities	(459,625)	(220,337)	(108,524)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repayment of debt assumed in acquisition of FacilitySource	(26,295)
Acquisition of businesses (cash paid for acquisitions more than three months after purchase date)	(16,774)	(19,854)	(1,125)
Decrease (increase) in intercompany receivables, net	233,975	(338,396)	(68,422)
Other financing activities, net	(16)	(3,145)	(1,173)
Net cash used in financing activities	190,890	(361,395)	(70,720)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS AND RESTRICTED CASH	160,805	(156,945)	117,257
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, AT BEGINNING OF PERIOD	114,143	271,088	153,831
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, AT END OF PERIOD	274,948	114,143	271,088
Cash paid during the period for:
Income taxes, net	198,930	198,520	174,164
Nonguarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	574,025	342,293	259,734
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(87,133)	(56,695)	(76,156)
Acquisition of businesses, including net assets acquired, intangibles and goodwill, net of cash acquired	(17,258)	(31,179)	(18,886)
Contributions to unconsolidated subsidiaries	(11,756)	(5,581)	(19,624)
Distributions from unconsolidated subsidiaries	4,440	10,768	7,435
Net proceeds from disposition of real estate held for investment	14,174		44,326
Other investing activities, net	(3,526)	424	20,905
Net cash used in investing activities	(101,059)	(82,263)	(42,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from senior term loans	452,745
Proceeds from notes payable on real estate	7,599	4,333	25,001
Repayment of notes payable on real estate	(19,058)	(12,556)	(38,046)
Acquisition of businesses (cash paid for acquisitions more than three months after purchase date)	(1,886)	(4,152)	(19,909)
Non-controlling interest contributions	25,355	5,301	2,272
Non-controlling interest distributions	(13,413)	(8,715)	(19,133)
Payment of financing costs	(1,876)	(21)	(159)
Decrease (increase) in intercompany receivables, net	(1,035,025)	(121,912)	(47,460)
Other financing activities, net	(2,706)	(9)	(185)
Net cash used in financing activities	(588,265)	(137,731)	(97,619)
Effect of currency exchange rate changes on cash and cash equivalents and restricted cash	(24,840)	29,338	(27,539)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS AND RESTRICTED CASH	(140,139)	151,637	92,576
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, AT BEGINNING OF PERIOD	695,065	543,428	450,852
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, AT END OF PERIOD	554,926	695,065	543,428
Cash paid during the period for:
Interest	1,674	92	3,195
Income taxes, net	$ 176,919	$ 158,477	$ 120,684

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The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

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Amount of cash outflow to a noncontrolling interest. Includes, but not limited to, reduction of noncontrolling interest ownership. Excludes dividends paid to the noncontrolling interest.

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Amount of distribution received from equity method investee for return of investment, classified as investing activities. Excludes distribution for return on investment, classified as operating activities.

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Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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Amount of cash inflow from a noncontrolling interest. Includes, but is not limited to, purchase of additional shares or other increase in noncontrolling interest ownership.

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Amount of cash inflow (outflow) from financing activities classified as other.

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Amount of cash inflow (outflow) from long-term debt by a related party. Related parties, include, but are not limited to, affiliates, owners or officers and their immediate families, and pension trusts.

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Amount of cash inflow (outflow) from long-term debt wholly or partially secured by collateral. Excludes tax exempt secured debt.

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Amount of cash inflow from sale of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Cash received from the sale of real estate that is held for investment, that is, it is part of an investing activity during the period.

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The cash outflow from the repayments of a long-term debt originally issued by another party but is assumed by the entity.

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Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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The cash outflow to repay long-term debt that is wholly or partially secured by collateral. Excludes repayments of tax exempt secured debt.

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The cash outflow for a long-term debt where the holder has highest claim on the entity's asset in case of bankruptcy or liquidation during the period.

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