Real Estate and Accumulated Depreciation - Real Estate and Accumulated Depreciation Gross (Details)	Sep. 30, 2016 USD ($)	[1],[2]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	$ 165,375,315
Building & Improvements	1,005,938,180
Total	1,171,313,495
Industrial Building [Member] | Monaca (Pittsburgh), PA [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	401,716
Building & Improvements	7,404,507
Total	7,806,223
Industrial Building [Member] | Orangeburg (New York), NY [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	694,720
Building & Improvements	3,200,955
Total	3,895,675
Industrial Building [Member] | Richland (Jackson), MS [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	218,000
Building & Improvements	1,640,591
Total	1,858,591
Industrial Building [Member] | Urbandale (Des Moines),IA [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	310,000
Building & Improvements	1,851,895
Total	2,161,895
Industrial Building [Member] | Richland (Jackson), MS [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	211,000
Building & Improvements	1,689,691
Total	1,900,691
Industrial Building [Member] | O'Fallon (St. Louis) MO [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	264,000
Building & Improvements	3,981,913
Total	4,245,913
Industrial Building [Member] | Fayetteville [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	172,000
Building & Improvements	5,269,876
Total	5,441,876
Industrial Building [Member] | Schaumburg (Chicago), IL [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,039,800
Building & Improvements	3,941,614
Total	4,981,414
Industrial Building [Member] | Burr Ridge (Chicago), IL [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	270,000
Building & Improvements	1,422,901
Total	1,692,901
Industrial Building [Member] | Romulus (Detroit), MI [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	531,000
Building & Improvements	4,069,532
Total	4,600,532
Industrial Building [Member] | Liberty, (Kansas City), MO [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	723,000
Building & Improvements	6,674,881
Total	7,397,881
Industrial Building [Member] | Omaha, NE [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,170,000
Building & Improvements	4,774,691
Total	5,944,691
Industrial Building [Member] | Charlottesville, VA [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,170,000
Building & Improvements	3,178,499
Total	4,348,499
Industrial Building [Member] | Jacksonville, FL (FDX) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,165,000
Building & Improvements	5,081,404
Total	6,246,404
Industrial Building [Member] | West Chester Twp (Cincinnati), OH [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	695,000
Building & Improvements	5,033,690
Total	5,728,690
Industrial Building [Member] | Richmond, VA (FDX) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,160,000
Building & Improvements	6,598,181
Total	7,758,181
Industrial Building [Member] | St. Joseph, MO [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	800,000
Building & Improvements	12,433,706
Total	13,233,706
Industrial Building [Member] | Newington (Hartford), CT [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	410,000
Building & Improvements	3,053,824
Total	3,463,824
Industrial Building [Member] | Cudahy (Milwaukee), WI [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	980,000
Building & Improvements	8,402,361
Total	9,382,361
Industrial Building [Member] | Beltsville (Washington DC), MD [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	3,200,000
Building & Improvements	11,312,355
Total	14,512,355
Industrial Building [Member] | Granite City (St. Louis, MO), IL [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	340,000
Building & Improvements	12,202,814
Total	12,542,814
Industrial Building [Member] | Winston-Salem, NC [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	980,000
Building & Improvements	6,258,613
Total	7,238,613
Industrial Building [Member] | Elgin (Chicago), IL [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,280,000
Building & Improvements	5,652,916
Total	6,932,916
Industrial Building [Member] | Tolleson (Phoenix), AZ [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,316,075
Building & Improvements	15,508,151
Total	16,824,226
Industrial Building [Member] | Ft. Myers, FL [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,910,000
Building & Improvements	3,107,447
Total	5,017,447
Industrial Building [Member] | Edwardsville (Kansas City), KS (Carlisle) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,185,000
Building & Improvements	6,040,401
Total	7,225,401
Industrial Building [Member] | Tampa (FDX) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	5,000,000
Building & Improvements	14,696,102
Total	19,696,102
Industrial Building [Member] | Denver, CO [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,150,000
Building & Improvements	5,204,051
Total	6,354,051
Industrial Building [Member] | Hanahan (Charleston), SC (SAIC) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,129,000
Building & Improvements	12,211,592
Total	13,340,592
Industrial Building [Member] | Hanahan (Charleston), SC (FDX Ground) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	930,000
Building & Improvements	6,684,653
Total	7,614,653
Industrial Building [Member] | Augusta, GA (FDX Ground) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	614,406
Building & Improvements	4,739,628
Total	5,354,034
Industrial Building [Member] | Huntsville, AL [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	748,115
Building & Improvements	5,857,016
Total	6,605,131
Industrial Building [Member] | Richfield (Cleveland), OH [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	2,676,848
Building & Improvements	13,758,630
Total	16,435,478
Industrial Building [Member] | Colorado Springs, CO [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,270,000
Building & Improvements	5,934,472
Total	7,204,472
Industrial Building [Member] | Tampa, FL (FDX) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	2,830,000
Building & Improvements	4,762,861
Total	7,592,861
Industrial Building [Member] | Griffin (Atlanta), GA [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	760,000
Building & Improvements	14,108,857
Total	14,868,857
Industrial Building [Member] | Roanoke, VA (DHL) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,853,000
Building & Improvements	5,552,447
Total	7,405,447
Industrial Building [Member] | Orion, MI [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	4,649,971
Building & Improvements	18,235,665
Total	22,885,636
Industrial Building [Member] | Carlstadt, NJ (New York, NY) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,194,000
Building & Improvements	3,709,589
Total	4,903,589
Industrial Building [Member] | Wheeling (Chicago), IL [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	5,112,120
Building & Improvements	13,425,532
Total	18,537,652
Industrial Building [Member] | White Bear Lake (Minneapolis/St. Paul), MN [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,393,000
Building & Improvements	3,764,126
Total	5,157,126
Industrial Building [Member] | Cheektowaga (Buffalo),NY [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	4,796,765
Building & Improvements	6,164,058
Total	10,960,823
Industrial Building [Member] | Richmond, VA (Carrier) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	446,000
Building & Improvements	4,322,309
Total	4,768,309
Industrial Building [Member] | Montgomery (Chicago), IL [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	2,000,000
Building & Improvements	9,298,367
Total	11,298,367
Industrial Building [Member] | Tampa, FL (TB Grand Prix) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,867,000
Building & Improvements	3,810,982
Total	5,677,982
Industrial Building [Member] | Augusta (FDX) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	380,000
Building & Improvements	1,591,732
Total	1,971,732
Industrial Building [Member] | Lakeland, FL [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	261,000
Building & Improvements	1,721,532
Total	1,982,532
Industrial Building [Member] | El Paso, TX [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	3,225,195
Building & Improvements	9,205,997
Total	12,431,192
Industrial Building [Member] | Chattanooga, TN [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	300,000
Building & Improvements	4,712,203
Total	5,012,203
Industrial Building [Member] | Bedford Heights (Cleveland), OH [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	990,000
Building & Improvements	5,873,879
Total	6,863,879
Industrial Building [Member] | Kansas City, MO [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	660,000
Building & Improvements	4,140,474
Total	4,800,474
Industrial Building [Member] | Punta Gorda, FL [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	0
Building & Improvements	4,113,265
Total	4,113,265
Industrial Building [Member] | Cocoa, FL [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,881,316
Building & Improvements	12,246,133
Total	14,127,449
Industrial Building [Member] | Orlando, FL [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	2,200,000
Building & Improvements	6,354,432
Total	8,554,432
Industrial Building [Member] | Topeka, KS [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	0
Building & Improvements	3,679,843
Total	3,679,843
Industrial Building [Member] | Memphis, TN [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,240,887
Building & Improvements	13,380,000
Total	14,620,887
Industrial Building [Member] | Houston, TX [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,730,000
Building & Improvements	6,353,107
Total	8,083,107
Industrial Building [Member] | Carrollton (Dallas), TX [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,500,000
Building & Improvements	16,269,106
Total	17,769,106
Industrial Building [Member] | Ft. Mill (Charlotte, NC), SC [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,670,000
Building & Improvements	13,743,307
Total	15,413,307
Industrial Building [Member] | Lebanon (Nashville), TN [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	2,230,000
Building & Improvements	11,985,126
Total	14,215,126
Industrial Building [Member] | Rockford, IL (Sherwin-Williams) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,100,000
Building & Improvements	4,451,227
Total	5,551,227
Industrial Building [Member] | Edinburg, TX [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,000,000
Building & Improvements	10,423,872
Total	11,423,872
Industrial Building [Member] | Streetsboro (Cleveland), OH [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,760,000
Building & Improvements	17,840,000
Total	19,600,000
Industrial Building [Member] | Corpus Christi, TX [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	0
Building & Improvements	4,764,500
Total	4,764,500
Industrial Building [Member] | Halfmoon (Albany), NY [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,190,000
Building & Improvements	4,335,600
Total	5,525,600
Industrial Building [Member] | Lebanon (Cincinnati), OH [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	240,000
Building & Improvements	4,212,425
Total	4,452,425
Industrial Building [Member] | Olive Branch, MS [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	800,000
Building & Improvements	13,750,000
Total	14,550,000
Industrial Building [Member] | Oklahoma City, OK [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,410,000
Building & Improvements	11,170,262
Total	12,580,262
Industrial Building [Member] | Waco, TX [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,350,000
Building & Improvements	11,196,157
Total	12,546,157
Industrial Building [Member] | Livonia (Detroit), MI [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	320,000
Building & Improvements	13,442,030
Total	13,762,030
Industrial Building [Member] | Olive Branch, MS (Memphis, TN) (Milwaukee Tool) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	2,550,000
Building & Improvements	34,364,917
Total	36,914,917
Industrial Building [Member] | Roanoke, VA [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,740,000
Building & Improvements	8,460,000
Total	10,200,000
Industrial Building [Member] | Green Bay, WI [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	590,000
Building & Improvements	5,980,000
Total	6,570,000
Industrial Building [Member] | Stewartville (Rochester), MN [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	900,000
Building & Improvements	4,320,000
Total	5,220,000
Industrial Building [Member] | Tulsa, OK [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	790,000
Building & Improvements	2,958,031
Total	3,748,031
Industrial Building [Member] | Buckner (Louisville), KY [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	2,280,000
Building & Improvements	24,487,852
Total	26,767,852
Industrial Building [Member] | Edwardsville (Kansas City), KS (International Paper) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	2,750,000
Building & Improvements	15,544,108
Total	18,294,108
Industrial Building [Member] | Altoona, PA [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,200,000
Building & Improvements	7,808,650
Total	9,008,650
Industrial Building [Member] | Spring (Houston), TX [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,890,000
Building & Improvements	17,393,798
Total	19,283,798
Industrial Building [Member] | Indianapolis, IN (FDX Ground) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	3,500,000
Building & Improvements	20,446,000
Total	23,946,000
Industrial Building [Member] | Sauget, IL [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,890,000
Building & Improvements	13,314,950
Total	15,204,950
Industrial Building [Member] | Lindale (Tyler), TX [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	540,000
Building & Improvements	9,390,000
Total	9,930,000
Industrial Building [Member] | Kansas City, MO (Bunzl) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,000,000
Building & Improvements	8,600,000
Total	9,600,000
Industrial Building [Member] | Frankfort (Lexington), KY [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,850,000
Building & Improvements	26,150,000
Total	28,000,000
Industrial Building [Member] | Jacksonville, FL (FDX Ground) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	6,000,000
Building & Improvements	24,645,954
Total	30,645,954
Industrial Building [Member] | Monroe (Cincinnati), OH [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,800,000
Building & Improvements	11,137,000
Total	12,937,000
Industrial Building [Member] | Greenwood (Indianapolis), IN [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	2,250,000
Building & Improvements	35,250,391
Total	37,500,391
Industrial Building [Member] | Ft. Worth (Dallas), TX [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	8,200,000
Building & Improvements	27,100,832
Total	35,300,832
Industrial Building [Member] | Cincinnati, OH [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	800,000
Building & Improvements	5,950,000
Total	6,750,000
Industrial Building [Member] | Rockford, IL (B/E Aerospace) [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	480,000
Building & Improvements	4,620,000
Total	5,100,000
Industrial Building [Member] | Concord (Charlotte), NC [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	4,305,000
Building & Improvements	27,670,897
Total	31,975,897
Industrial Building [Member] | Covington (New Orleans), LA [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	2,720,000
Building & Improvements	15,690,000
Total	18,410,000
Industrial Building [Member] | Imperial (Pittsburgh), PA [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	3,700,000
Building & Improvements	16,250,000
Total	19,950,000
Industrial Building [Member] | Burlington (Seattle/Everett), WA [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	8,000,000
Building & Improvements	22,210,680
Total	30,210,680
Industrial Building [Member] | Colorado Springs, CO [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	2,150,000
Building & Improvements	26,350,000
Total	28,500,000
Industrial Building [Member] | Louisville, KY [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	1,590,000
Building & Improvements	9,714,000
Total	11,304,000
Industrial Building [Member] | Davenport (Orlando), FL [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	7,060,000
Building & Improvements	30,720,000
Total	37,780,000
Industrial Building [Member] | Olathe (Kansas City), KS [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	2,350,000
Building & Improvements	29,387,000
Total	31,737,000
Shopping Center [Member] | Somerset, NJ [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	34,316
Building & Improvements	3,038,565
Total	3,072,881
Vacant Land [Member] | Shelby County [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land	11,065
Building & Improvements	0
Total	$ 11,065

[1] See pages 145-147 for reconciliation.

[2] The aggregate cost for Federal tax purposes approximates historical cost.