Stockholders' Equity and Non-controlling Interests - Redeemable non-controlling interest in the Operating Partnership (Details) - USD ($)																						3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 13, 2017	Aug. 17, 2017	Aug. 10, 2017	Jul. 19, 2017	Jul. 14, 2017	Jul. 10, 2017	May 09, 2017	Apr. 14, 2017	Apr. 12, 2017	Mar. 27, 2017	Feb. 22, 2017	Jan. 13, 2017	Nov. 03, 2016	Oct. 14, 2016	Aug. 03, 2016	Jul. 15, 2016	May 25, 2016	May 09, 2016	Apr. 15, 2016	Mar. 08, 2016	Mar. 02, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Oct. 29, 2014
Change in redeemable non-controlling interest
Net loss attributable to non-controlling interests																									$ (64,000)
Redemption of units for common stock																									$ (9,519,000)
Redeemable non-controlling interests in operating partnership, preferred units																						$ 119,633,000		$ 119,633,000		$ 119,915,000
Series B Participating Preferred Stock																						$ 144,223,000		$ 144,223,000
Common Stock, Par or Stated Value Per Share																						$ 0.01		$ 0.01		$ 0.01
Cash dividend paid (in dollars per share)	$ 0.1275				$ 0.1275			$ 0.1275				$ 0.1275		$ 0.1275		$ 0.1275			$ 0.1275
Distributions per Common Share/OP unit (in dollars per share)				$ 0.1275			$ 0.1275				$ 0.1275		$ 0.1275		$ 0.1275			$ 0.1275		$ 0.1275		$ 0.1275	$ 0.1275	$ 0.3825	$ 0.3825	$ 0.5100
Repayment of principal																								$ 20,819,000	$ 84,750,000
Payments for repurchase of shares																								$ 7,446,000
Share repurchase
Change in redeemable non-controlling interest
Shares repurchased (in shares)																						841,257		841,257
Payments for repurchase of shares																						$ 7,400,000		$ 7,400,000
Shares repurchased, average price (in dollars per share)																						$ 8.85		$ 8.85
Share repurchase | Maximum
Change in redeemable non-controlling interest
Amount approved for share repurchase program																											$ 25,000,000
Common stock
Change in redeemable non-controlling interest
Distributions payable																								$ 730,000	724,000
Share repurchased and retired (in shares)																								841,000
Shares repurchased (in shares)				531,827		118,634			328,122	129,174
Redeemable OP Units
Change in redeemable non-controlling interest
Accrued distributions to non-controlling interest																									(113,000)
Redeemable OP Units | Common stock
Change in redeemable non-controlling interest
Opening balance																									$ 9,695,000	$ 9,695,000
Opening balance (in shares)																									884,000	884,000
Net loss attributable to non-controlling interests																									$ (64,000)
Accrued distributions to non-controlling interest																									$ (113,000)
Redemption of units for common stock (in shares)																									(884,000)
Redemption of units for common stock																									$ (9,518,000)
Ending balance
Ending balance (in shares)
Temporary Equity redeemable for cash																	883,724
Redeemable Preferred OP Units
Change in redeemable non-controlling interest
Accrued distributions to non-controlling interest																						$ (877,000)	$ (887,000)	$ (2,632,000)	(2,057,000)
Percentage of cumulative preferential dividends																								3.00%
Distributions payable																								$ 2,633,000	2,057,000
Redeemable Preferred OP Units | Preferred stock
Change in redeemable non-controlling interest
Opening balance																								$ 119,915,000
Opening balance (in shares)																								117,000
Issuance of units																									$ 117,000,000
Issuance of units (in shares)																									117,000
Accrued distributions to non-controlling interest																								$ 2,633,000	$ 2,057,000
Distributions paid																								(2,915,000)
Redeemable non-controlling interests in operating partnership, preferred units																						$ 119,633,000		$ 119,633,000
Ending balance																							$ 119,057,000		$ 119,057,000	$ 119,915,000
Ending balance (in shares)																						117,000	117,000	117,000	117,000	117,000
Series A Preferred Units
Change in redeemable non-controlling interest
Percentage of preferential cash distribution																					3.00%
Liquidation preference																					$ 1,000
Number of trading days																								20 days
Series A Preferred Units | Illinois | Asset acquisition
Stockholders’ Equity and Non-controlling Interests
Issuance of stock (in shares)																					117,000
Change in redeemable non-controlling interest
Liquidation value																						$ 119,600,000		$ 119,600,000		$ 119,900,000
Series B Participating Preferred Stock
Change in redeemable non-controlling interest
Accrued distributions to non-controlling interest																						(1,082,000)		$ (1,082,000)
Distributions paid																						$ 1,100,000
Percentage of cumulative change in the estimated value of farmland		50.00%
Final liquidation preference, percentage cap on total return		9.00%
Number of preceding years considered in redemption price calculation																								4 years
Constant percentage																								50.00%
Shares issued under underwriting agreement		6,037,500	6,037,500
Preference dividend (as a percent)		6.00%
Par value		$ 0.01
Common stock, issue price (in dollars per share)		25.00
Liquidation preference		$ 25
Repayment of principal			$ 1,100,000