STOCKHOLDERS' EQUITY (Narrative) (Details)							3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 14, 2018 USD ($) shares	Feb. 28, 2018 $ / shares	Jan. 26, 2018 USD ($) shares	Jun. 27, 2017 USD ($) shares	May 03, 2017 shares	Mar. 07, 2017 $ / shares	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2017 USD ($) shares	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2017 USD ($) shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 shares	Dec. 31, 2021 shares	Dec. 31, 2020 shares	Dec. 31, 2019 shares	Dec. 31, 2018 shares	Apr. 01, 2018 $ / shares	Mar. 31, 2018 shares	Mar. 29, 2018 USD ($) shares	Jan. 25, 2018 shares	Apr. 05, 2017 USD ($)	Mar. 31, 2017 shares	Jul. 27, 2016 USD ($) $ / shares	May 20, 2016 USD ($)	Apr. 30, 2015 shares
Class of Stock [Line Items]
Common stock, shares issued							19,254,141		19,254,141		14,429,055
Common stock, shares outstanding							19,254,141		19,254,141		14,429,055
Issuance of stock, net of offering costs (in shares)	4,600,000			4,025,000
Net proceeds from issuance of common stock | $	$ 81,100,000			$ 83,900,000					$ 81,831,000	$ 108,235,000
Preferred ATM shares, aggregate maximum offering price | $																			$ 45,000,000
Restricted stock expense, recognized | $									$ 1,200,000	$ 700,000
Number of shares repurchased and retired									213,078
Retirement of common stock | $									$ 3,200,000
Stock repurchase program, remaining authorized amount | $							$ 6,800,000		$ 6,800,000
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued							110,000		110,000		40,000
Preferred stock, shares outstanding							110,000		110,000		40,000
Preferred stock, shares authorized							300,000		300,000		300,000
Value of shares to be issued prior to expiration of commitment period | $									$ 50,000,000
Amount of preferred shares issuable in future | $																							$ 125,000,000
Percentage of increase in book value									25.00%
Internal rate of return to the preferred shareholders									14.00%
Preferred stock, par value | $ / shares							$ 0.01		$ 0.01		$ 0.01												$ 0.01
Preferred stock, liquidation preferance per share | $ / shares																							$ 1,000
Preferred stock, dividend rate									7.00%		7.00%
Preferred stock redemption terms									The Series A Preferred Stock may be redeemed at the Company's option (i) after five years from the Effective Date at a price equal to 105% of the Liquidation Value per share plus the value of all accumulated and unpaid Cash Distributions and Stock Dividends, and (ii) after six years from the Effective Date at a price equal to 100% of the Liquidation Value per share plus the value of all accumulated and unpaid Cash Distributions and Stock Dividends. In the event of certain change of control events affecting the Company prior to the third anniversary of the Effective Date, the Company must redeem all shares of Series A Preferred Stock for a price equal to (a) the Liquidation Value, plus (b) accumulated and unpaid Cash Distributions and Stock Dividends, plus (c) a make-whole premium designed to provide the holders of the Series A Preferred Stock with a return on the redeemed shares equal to a 14.0% internal rate of return through the third anniversary of the Effective Date.
Debt instrument covenant debt to total intangible asset ratio									0.4
Proceeds from issuance of preferred stock | $									$ 69,963,000
Dividends declared date		Feb. 28, 2018				May 02, 2018
Dividend payable, amount per share | $ / shares		$ 12.12				$ 16.07
Dividends payable date		Apr. 13, 2018				Jul. 13, 2018
Dividends payable, date of record		Apr. 01, 2018				Jul. 01, 2018
Series A Preferred Stock [Member] | Scenario, Plan [Member]
Class of Stock [Line Items]
Percentage of increase in book value									25.00%
Internal rate of return to the preferred shareholders									14.00%
Preferred stock forcasted dividend payable | $									$ 2,125,000
Series A Preferred Stock [Member] | Until Sixth Anniversary [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate									7.00%
Series A Preferred Stock [Member] | After Sixth Anniversary [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate									8.50%
Series A Preferred Stock [Member] | Occurrence of certain triggering events [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate									5.00%
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued			1,500,000				1,571,734		1,571,734		0
Preferred stock, shares outstanding							1,571,734		1,571,734		0
Preferred stock, shares authorized							3,750,000		3,750,000		3,750,000									1,725,000
Preferred stock, par value | $ / shares							$ 0.01		$ 0.01		$ 0.01
Preferred stock, liquidation preferance per share | $ / shares							$ 25.00		$ 25.00
Preferred stock, dividend rate									7.00%		7.00%
Preferred stock redemption terms									On or after January 26, 2023, the Series B Preferred Stock may be redeemed, at the Company's option, upon not less than 30 nor more than 60 days' written notice, in whole or in part, at any time and from time to time, for cash at a redemption price equal to $25.00 per share, plus any accrued and unpaid dividends (whether or not authorized or declared) to, but excluding, the date fixed for redemption. Holders of Series B Preferred Stock will have no right to require the redemption or repurchase of the Series B Preferred Stock. Upon the occurrence of a Change of Control (as defined in the Series B Articles Supplementary), we may redeem for cash, in whole or in part, the Series B Preferred Stock within 120 days after the date on which such Change of Control occurred, by paying $25.00 per share, plus any accrued and unpaid dividends (whether or not authorized or declared) to, but excluding, the date fixed for redemption
Proceeds from issuance of preferred stock | $			$ 36,000,000						$ 37,463,000
Preferred stock, dividend rate per share | $ / shares									$ 1.7500
Preferred stock share cap rate | $									2.74876
Maximum [Member]
Class of Stock [Line Items]
Stock repurchase program, authorized amount | $																								$ 10,000,000
Maximum [Member] | Series A Preferred Stock [Member]
Class of Stock [Line Items]
Amount of preferred shares issuable in future | $																							$ 35,000,000
Maximum [Member] | Series A Preferred Stock [Member] | Monthly Increments [Member]
Class of Stock [Line Items]
Amount of preferred shares issuable in future | $																							15,000,000
Minimum [Member] | Series A Preferred Stock [Member] | Monthly Increments [Member]
Class of Stock [Line Items]
Amount of preferred shares issuable in future | $																							$ 5,000,000
Restricted Stock [Member]
Class of Stock [Line Items]
Nonvested restricted stock							172,499	202,502	172,499	202,502	185,002	120,001						195,502				120,001
Number of shares granted							57,333	111,414	75,333	111,414
Number of shares, vested							80,336	28,913	87,836	28,913
Restricted stock expense, recognized | $							$ 800,000	$ 400,000
Number of shares forfeited
Restricted Stock [Member] | Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued							110,000		110,000
Proceeds from issuance of preferred stock | $									$ 110,000,000
Non Employee Director [Member] | Restricted Stock [Member]
Class of Stock [Line Items]
Expenses related to restricted stock awards, period for recognition									2 years 3 months 18 days		2 years 3 months 18 days
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options | $							$ 2,900,000		$ 2,900,000		$ 2,700,000
Equity Incentive Plan 2015 [Member] | Restricted Stock [Member]
Class of Stock [Line Items]
Shares reserved for future issuance																									200,000
Shares reserved for issuance					370,000
Number of shares increased (decreased) related to share base payment plan					170,000
Amended and Restated 2015 Equity Incentive Plan [Member] | Restricted Stock [Member]
Class of Stock [Line Items]
Number of shares granted									363,587		288,254
Amended and Restated 2015 Equity Incentive Plan [Member] | Restricted Stock [Member] | Maximum [Member]
Class of Stock [Line Items]
Equity award vesting period									5 years
Amended and Restated 2015 Equity Incentive Plan [Member] | Restricted Stock [Member] | Minimum [Member]
Class of Stock [Line Items]
Equity award vesting period									3 years
Amended and Restated 2015 Equity Incentive Plan [Member] | Non Employee Director [Member] | Restricted Stock [Member]
Class of Stock [Line Items]
Number of shares, vested									87,836		46,413	55,172
Number of shares forfeited												1,667
Amended and Restated 2015 Equity Incentive Plan [Member] | Non Employee Director [Member] | Restricted Stock [Member] | Scenario, Forecast [Member]
Class of Stock [Line Items]
Number of shares vested or expected to vest													17,502
Amended and Restated 2015 Equity Incentive Plan [Member] | Non Employee Director [Member] | Restricted Stock [Member] | Share-based Compensation Award, Tranche Two [Member] | Scenario, Forecast [Member]
Class of Stock [Line Items]
Number of shares vested or expected to vest																10,000
Amended and Restated 2015 Equity Incentive Plan [Member] | Non Employee Director [Member] | Restricted Stock [Member] | Share-based Compensation Award, Tranche Three [Member] | Scenario, Forecast [Member]
Class of Stock [Line Items]
Number of shares vested or expected to vest															72,500
Amended and Restated 2015 Equity Incentive Plan [Member] | Non Employee Director [Member] | Restricted Stock [Member] | Share Based Compensation Award Tranche Four [Member] | Scenario, Forecast [Member]
Class of Stock [Line Items]
Number of shares vested or expected to vest														72,497
ATM Program [Member]
Class of Stock [Line Items]
Issuance of stock, net of offering costs (in shares)									1,323,722
Net proceeds from issuance of common stock | $									$ 28,500,000
Stock repurchase program, authorized amount | $																					$ 50,000,000
Shares issued, price per share | $ / shares							$ 22.24		$ 22.24
ATM Program [Member] | Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued							71,734		71,734
Preferred stock, shares authorized																			2,025,000
Proceeds from issuance of preferred stock | $									$ 1,500,000
Shares issued, price per share | $ / shares							$ 22.94		$ 22.94
Common Stock [Member]
Class of Stock [Line Items]
Issuance of stock, net of offering costs (in shares)									4,600,000	4,025,000
Issuances of stock-based awards (in shares)									75,333	111,414
Accounting Standards Update 2018-07 [Member]
Class of Stock [Line Items]
Grant date fair value of non-vested awards | $ / shares																	$ 18.10