CONDENSED CONSOLIDATING INFORMATION (Unaudited) - Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Net real estate investments	$ 20,596,963	$ 22,092,452
Cash and cash equivalents	86,107	81,355
Escrow deposits and restricted cash	62,440	106,898
Investment in and advances to affiliates	0	0
Goodwill	1,045,877	1,034,644
Assets held for sale	24,180	65,413
Other assets	782,386	573,779
Total assets	22,597,953	23,954,541
Liabilities:
Senior notes payable and other debt	10,478,455	11,276,062
Intercompany loans	0	0
Accrued interest	76,883	93,958
Accounts payable and other liabilities	1,134,898	1,183,489
Liabilities related to assets held for sale	14,790	60,265
Deferred income taxes	236,616	250,092
Total liabilities	11,941,642	12,863,866
Redeemable OP Unitholder and noncontrolling interests	143,242	158,490
Total equity	10,513,069	10,932,185	$ 10,528,753
Total liabilities and equity	22,597,953	23,954,541
Consolidated Elimination
Assets
Net real estate investments	0	0
Cash and cash equivalents	0	0
Escrow deposits and restricted cash	0	0
Investment in and advances to affiliates	(18,147,345)	(17,706,597)
Goodwill	0	0
Assets held for sale	0	0
Other assets	0	0
Total assets	(18,147,345)	(17,706,597)
Liabilities:
Senior notes payable and other debt	0	0
Intercompany loans	0	0
Accrued interest	0	0
Accounts payable and other liabilities	0	0
Liabilities related to assets held for sale	0	0
Deferred income taxes	0	0
Total liabilities	0	0
Redeemable OP Unitholder and noncontrolling interests	0	0
Total equity	(18,147,345)	(17,706,597)
Total liabilities and equity	(18,147,345)	(17,706,597)
Ventas, Inc.
Assets
Net real estate investments	3,634	1,844
Cash and cash equivalents	8,291	7,129
Escrow deposits and restricted cash	5,198	39,816
Investment in and advances to affiliates	15,421,147	14,790,537
Goodwill	0	0
Assets held for sale	0	0
Other assets	57,960	55,934
Total assets	15,496,230	14,895,260
Liabilities:
Senior notes payable and other debt	0	0
Intercompany loans	8,066,423	7,838,898
Accrued interest	(8,976)	(6,410)
Accounts payable and other liabilities	355,472	377,536
Liabilities related to assets held for sale	0	0
Deferred income taxes	586	608
Total liabilities	8,413,505	8,210,632
Redeemable OP Unitholder and noncontrolling interests	12,399	12,237
Total equity	7,070,326	6,672,391
Total liabilities and equity	15,496,230	14,895,260
Ventas Realty
Assets
Net real estate investments	112,869	119,508
Cash and cash equivalents	0	0
Escrow deposits and restricted cash	128	128
Investment in and advances to affiliates	2,726,198	2,916,060
Goodwill	0	0
Assets held for sale	0	0
Other assets	6,669	9,458
Total assets	2,845,864	3,045,154
Liabilities:
Senior notes payable and other debt	8,330,288	8,895,641
Intercompany loans	(5,390,219)	(7,127,547)
Accrued interest	66,613	77,691
Accounts payable and other liabilities	24,843	24,635
Liabilities related to assets held for sale	0	0
Deferred income taxes	0	0
Total liabilities	3,031,525	1,870,420
Redeemable OP Unitholder and noncontrolling interests	0	0
Total equity	(185,661)	1,174,734
Total liabilities and equity	2,845,864	3,045,154
Ventas Subsidiaries
Assets
Net real estate investments	20,480,460	21,971,100
Cash and cash equivalents	77,816	74,226
Escrow deposits and restricted cash	57,114	66,954
Investment in and advances to affiliates	0	0
Goodwill	1,045,877	1,034,644
Assets held for sale	24,180	65,413
Other assets	717,757	508,387
Total assets	22,403,204	23,720,724
Liabilities:
Senior notes payable and other debt	2,148,167	2,380,421
Intercompany loans	(2,676,204)	(711,351)
Accrued interest	19,246	22,677
Accounts payable and other liabilities	754,583	781,318
Liabilities related to assets held for sale	14,790	60,265
Deferred income taxes	236,030	249,484
Total liabilities	496,612	2,782,814
Redeemable OP Unitholder and noncontrolling interests	130,843	146,253
Total equity	21,775,749	20,791,657
Total liabilities and equity	$ 22,403,204	$ 23,720,724