Stockholders' Equity - Narrative - Share Repurchase Plan and Redeemable Common Stock (Details) - Share Repurchase Plan [Member]	12 Months Ended
	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) asset shares	Sep. 30, 2017 shares
Class of Stock [Line Items]
Number of company assets sold that constitute a return of capital as a result of such sale. | asset		1
Notice period for amendment, suspension, or termination of stock repurchase plan.	30 days
Common Stock [Member]
Class of Stock [Line Items]
Number of shares that can be repurchased before the first anniversary of date of purchase | shares			0
Share repurchase plan, disability or death holding period exemption period, maximum		2 years
Stock repurchase plan, minimum redemption notice period	15 days
Stock repurchase plan, settlement period	30 days
Minimum number of days prior to repurchase date a repurchase request may be withdrawn		3 days
Shares redeemed (in shares) | shares	836,770	730,953
Stock repurchase plan, stock redeemed, value | $	$ 8,000,000	$ 8,000,000
Stock requested for redemption (in shares) | shares	2,786,995	2,521,337
Stock requested for redemption, value | $	$ 24,955,829	$ 28,904,491
Stock requested for redemption, outstanding (in shares) | shares	5,050,946	3,100,720
Stock requested for redemption, redemptions payable | $	$ 46,417,038	$ 36,198,922
Maximum percentage of weighted average shares outstanding in prior calendar period that may be repurchased in current calendar period	5.00%
Common Stock [Member] | Accounts Payable and Accrued Liabilities [Member]
Class of Stock [Line Items]
Stock requested for redemption, redemptions payable | $	$ 2,000,000