CONSOLIDATING FINANCIAL STATEMENTS (Balance Sheets) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
CURRENT ASSETS
Cash and cash equivalents	$ 146,259	$ 112,653
Accounts receivable, less allowance for doubtful accounts	43,089	27,693
Inventory	26,950	24,141
Prepaid expenses	15,849	15,993
Other current assets	2,443	3,047
Total current assets	234,590	183,527
TIMBER AND TIMBERLANDS, NET OF DEPLETION AND AMORTIZATION	2,386,949	2,462,066
HIGHER AND BETTER USE TIMBERLANDS AND REAL ESTATE DEVELOPMENT COSTS	79,747	80,797
NET PROPERTY, PLANT AND EQUIPMENT	22,802	23,378
RESTRICTED CASH	45,418	59,703
INVESTMENT IN SUBSIDIARIES	0	0
INTERCOMPANY RECEIVABLE	0	0
OTHER ASSETS	72,709	49,010
TOTAL ASSETS	2,842,215	2,858,481
CURRENT LIABILITIES
Accounts payable	22,406	25,148
Current maturities of long-term debt	0	3,375
Accrued taxes	7,818	3,781
Accrued payroll and benefits	8,320	9,662
Accrued interest	7,963	5,054
Deferred revenue	13,867	9,721
Other current liabilities	21,249	11,807
Total current liabilities	81,623	68,548
LONG-TERM DEBT, NET OF DEFERRED FINANCING COSTS	972,426	1,022,004
PENSION AND OTHER POSTRETIREMENT BENEFITS	28,925	31,905
OTHER NON-CURRENT LIABILITIES	58,142	43,084
INTERCOMPANY PAYABLE	0	0
TOTAL RAYONIER INC. SHAREHOLDERS’ EQUITY	1,600,300	1,593,023
Noncontrolling interest	100,799	99,917
TOTAL SHAREHOLDERS’ EQUITY	1,701,099	1,692,940	$ 1,496,752
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	2,842,215	2,858,481
Consolidating Adjustments
CURRENT ASSETS
Cash and cash equivalents	0	0
Accounts receivable, less allowance for doubtful accounts	0	0
Inventory	0	0
Prepaid expenses	0	0
Other current assets	0	0
Total current assets	0	0
TIMBER AND TIMBERLANDS, NET OF DEPLETION AND AMORTIZATION	0	0
HIGHER AND BETTER USE TIMBERLANDS AND REAL ESTATE DEVELOPMENT COSTS	0	0
NET PROPERTY, PLANT AND EQUIPMENT	0	0
RESTRICTED CASH	0	0
INVESTMENT IN SUBSIDIARIES	(4,906,818)	(4,345,564)
INTERCOMPANY RECEIVABLE	0	0
OTHER ASSETS	0	0
TOTAL ASSETS	(4,906,818)	(4,345,564)
CURRENT LIABILITIES
Accounts payable	0	0
Current maturities of long-term debt		0
Accrued taxes	0	0
Accrued payroll and benefits	0	0
Accrued interest	0	0
Deferred revenue	0	0
Other current liabilities	0	0
Total current liabilities	0	0
LONG-TERM DEBT, NET OF DEFERRED FINANCING COSTS	0	0
PENSION AND OTHER POSTRETIREMENT BENEFITS	0	0
OTHER NON-CURRENT LIABILITIES	0	0
INTERCOMPANY PAYABLE	0	0
TOTAL RAYONIER INC. SHAREHOLDERS’ EQUITY	(4,906,818)	(4,345,564)
Noncontrolling interest	0	0
TOTAL SHAREHOLDERS’ EQUITY	(4,906,818)	(4,345,564)
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	(4,906,818)	(4,345,564)
Rayonier Inc. (Parent Issuer) | Reportable Legal Entities
CURRENT ASSETS
Cash and cash equivalents	6,245	48,564
Accounts receivable, less allowance for doubtful accounts	1,994	0
Inventory	0	0
Prepaid expenses	0	0
Other current assets	0	0
Total current assets	8,239	48,564
TIMBER AND TIMBERLANDS, NET OF DEPLETION AND AMORTIZATION	0	0
HIGHER AND BETTER USE TIMBERLANDS AND REAL ESTATE DEVELOPMENT COSTS	0	0
NET PROPERTY, PLANT AND EQUIPMENT	0	0
RESTRICTED CASH	0	0
INVESTMENT IN SUBSIDIARIES	1,875,187	1,531,156
INTERCOMPANY RECEIVABLE	48,671	40,067
OTHER ASSETS	2	2
TOTAL ASSETS	1,932,099	1,619,789
CURRENT LIABILITIES
Accounts payable	0	0
Current maturities of long-term debt		0
Accrued taxes	0	0
Accrued payroll and benefits	0	0
Accrued interest	6,094	3,047
Deferred revenue	0	0
Other current liabilities	1,994	0
Total current liabilities	8,088	3,047
LONG-TERM DEBT, NET OF DEFERRED FINANCING COSTS	323,711	323,434
PENSION AND OTHER POSTRETIREMENT BENEFITS	0	0
OTHER NON-CURRENT LIABILITIES	0	0
INTERCOMPANY PAYABLE	0	(299,715)
TOTAL RAYONIER INC. SHAREHOLDERS’ EQUITY	1,600,300	1,593,023
Noncontrolling interest	0	0
TOTAL SHAREHOLDERS’ EQUITY	1,600,300	1,593,023
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	1,932,099	1,619,789
Subsidiary Guarantors | Reportable Legal Entities
CURRENT ASSETS
Cash and cash equivalents	92,747	25,042
Accounts receivable, less allowance for doubtful accounts	2,738	3,726
Inventory	0	0
Prepaid expenses	1,534	759
Other current assets	106	14
Total current assets	97,125	29,541
TIMBER AND TIMBERLANDS, NET OF DEPLETION AND AMORTIZATION	0	0
HIGHER AND BETTER USE TIMBERLANDS AND REAL ESTATE DEVELOPMENT COSTS	0	0
NET PROPERTY, PLANT AND EQUIPMENT	17,198	21
RESTRICTED CASH	0	0
INVESTMENT IN SUBSIDIARIES	3,031,631	2,814,408
INTERCOMPANY RECEIVABLE	(629,661)	(628,167)
OTHER ASSETS	37,532	12,680
TOTAL ASSETS	2,553,825	2,228,483
CURRENT LIABILITIES
Accounts payable	4,210	2,838
Current maturities of long-term debt		0
Accrued taxes	180	48
Accrued payroll and benefits	4,891	5,298
Accrued interest	1,869	1,995
Deferred revenue	0	0
Other current liabilities	1,029	564
Total current liabilities	12,179	10,743
LONG-TERM DEBT, NET OF DEFERRED FINANCING COSTS	648,715	663,570
PENSION AND OTHER POSTRETIREMENT BENEFITS	29,609	32,589
OTHER NON-CURRENT LIABILITIES	7,096	9,386
INTERCOMPANY PAYABLE	(18,961)	(18,961)
TOTAL RAYONIER INC. SHAREHOLDERS’ EQUITY	1,875,187	1,531,156
Noncontrolling interest	0	0
TOTAL SHAREHOLDERS’ EQUITY	1,875,187	1,531,156
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	2,553,825	2,228,483
Non- guarantors | Reportable Legal Entities
CURRENT ASSETS
Cash and cash equivalents	47,267	39,047
Accounts receivable, less allowance for doubtful accounts	38,357	23,967
Inventory	26,950	24,141
Prepaid expenses	14,315	15,234
Other current assets	2,337	3,033
Total current assets	129,226	105,422
TIMBER AND TIMBERLANDS, NET OF DEPLETION AND AMORTIZATION	2,386,949	2,462,066
HIGHER AND BETTER USE TIMBERLANDS AND REAL ESTATE DEVELOPMENT COSTS	79,747	80,797
NET PROPERTY, PLANT AND EQUIPMENT	5,604	23,357
RESTRICTED CASH	45,418	59,703
INVESTMENT IN SUBSIDIARIES	0	0
INTERCOMPANY RECEIVABLE	580,990	588,100
OTHER ASSETS	35,175	36,328
TOTAL ASSETS	3,263,109	3,355,773
CURRENT LIABILITIES
Accounts payable	18,196	22,310
Current maturities of long-term debt		3,375
Accrued taxes	7,638	3,733
Accrued payroll and benefits	3,429	4,364
Accrued interest	0	12
Deferred revenue	13,867	9,721
Other current liabilities	18,226	11,243
Total current liabilities	61,356	54,758
LONG-TERM DEBT, NET OF DEFERRED FINANCING COSTS	0	35,000
PENSION AND OTHER POSTRETIREMENT BENEFITS	(684)	(684)
OTHER NON-CURRENT LIABILITIES	51,046	33,698
INTERCOMPANY PAYABLE	18,961	318,676
TOTAL RAYONIER INC. SHAREHOLDERS’ EQUITY	3,031,631	2,814,408
Noncontrolling interest	100,799	99,917
TOTAL SHAREHOLDERS’ EQUITY	3,132,430	2,914,325
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	$ 3,263,109	$ 3,355,773