Loans Payable - Summary of Loans Payable (Details) - USD ($) | Jun. 28, 2018 | Jun. 19, 2018 | Jun. 15, 2018 | May 23, 2018 | Mar. 11, 2018 | Jan. 10, 2018 | Jun. 30, 2018 | May 14, 2018 | May 03, 2018 | Dec. 31, 2017 |
Debt Instrument [Line Items] | | | | | | | | | | |
Mortgages and other indebtedness | | | | | | | $ 365,922,000 | | | $ 307,375,000 |
Total Principal Balance | | | | | | | 371,449,000 | | | 313,031,000 |
Unamortized debt issuance cost | | | | | | | (5,527,000) | | | (5,656,000) |
Monarch Bank Line Of Credit | LIBOR | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, basis spread on variable rate | | | 3.50% | | | 3.00% | | | | |
Lumber River | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | $ 10,723 | | | | 10,723 | | | |
Debt instrument, interest rate. stated percentage | | | 3.50% | | | | | | | |
Mortgages and other indebtedness | | | $ 1,480,000 | | | | $ 1,471,000 | | | 1,500,000 |
Lumber River | LIBOR | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, basis spread on variable rate | | | | | | | 3.50% | | | |
Harbor Point | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 11,024 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 5.85% | | | |
Perimeter Square | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 5.50% | | | |
Mortgages and other indebtedness | | | | | | | $ 6,192,000 | | | 5,382,000 |
Riversedge North | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 8,802 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 6.00% | | | |
Mortgages and other indebtedness | | | | | | | $ 836,000 | | | 863,000 |
Monarch Bank Building | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 7,340 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.85% | | | |
Mortgages and other indebtedness | | | | | | | | | | 1,266,000 |
DF I-Moyock | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 10,665 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 5.00% | | | |
Rivergate | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 141,547 | | | |
Mortgages and other indebtedness | | | | | | | $ 22,403,000 | | | 22,689,000 |
Rivergate | LIBOR | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, basis spread on variable rate | | | | | | | 2.95% | | | |
LaGrange Marketplace | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 15,065 | | | |
Mortgages and other indebtedness | | | | | | | $ 0 | | | 2,317,000 |
LaGrange Marketplace | LIBOR | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, basis spread on variable rate | | | | | | | 3.75% | | | |
Folly Road | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 32,827 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.00% | | | |
Mortgages and other indebtedness | | | | | | | $ 6,145,000 | | | 6,181,000 |
Columbia Fire House construction loan | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.00% | | | |
Mortgages and other indebtedness | | | | | | | $ 4,174,000 | | | 3,421,000 |
Shoppes at TJ Maxx | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 33,880 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 3.88% | | | |
Mortgages and other indebtedness | | | | | | | $ 5,634,000 | | | 5,727,000 |
JANAF Bravo | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.65% | | | |
Mortgages and other indebtedness | | | | | | | $ 6,500,000 | | | 0 |
Walnut Hill Plaza | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 5.50% | | | |
Mortgages and other indebtedness | | | | | | | $ 3,903,000 | | | 3,903,000 |
Twin City Commons | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 17,827 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.86% | | | |
Mortgages and other indebtedness | | | | | | | $ 3,080,000 | | | 3,111,000 |
Shoppes at Eagle Harbor | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | $ 26,528 | | $ 26,528 | | | |
Debt instrument, interest rate. stated percentage | | | | | 5.10% | | 5.10% | | | |
Mortgages and other indebtedness | | | | | $ 3,320,000 | | | | | 3,341,000 |
New Market | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | $ 48,747 | | | $ 48,747 | | | |
Debt instrument, interest rate. stated percentage | | | | 5.65% | | | 5.65% | | | |
Mortgages and other indebtedness | | | | $ 7,000,000 | | | $ 7,000,000 | | | 0 |
Deutsche Bank | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | $ 33,340 | | | | | | $ 33,340 | | | |
Debt instrument, interest rate. stated percentage | 5.71% | | | | | | 5.71% | | | |
Mortgages and other indebtedness | $ 5,740,000 | | | | | | $ 5,740,000 | | | 0 |
JANAF | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 333,159 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.49% | | | |
Mortgages and other indebtedness | | | | | | | $ 53,048,000 | | | 0 |
Tampa Festival | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 50,797 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 5.56% | | | |
Mortgages and other indebtedness | | | | | | | $ 8,298,000 | | | 8,368,000 |
Forrest Gallery | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 50,973 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 5.40% | | | |
Mortgages and other indebtedness | | | | | | | $ 8,600,000 | | | 8,669,000 |
South Carolina Food Lions Note | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 68,320 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 5.25% | | | |
Mortgages and other indebtedness | | | | | | | $ 11,960,000 | | | 12,050,000 |
Cypress Shopping Center | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 34,360 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.70% | | | |
Mortgages and other indebtedness | | | | | | | $ 6,432,000 | | | 6,485,000 |
Port Crossing | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 34,788 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.84% | | | |
Mortgages and other indebtedness | | | | | | | $ 6,207,000 | | | 6,263,000 |
Freeway Junction | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 41,798 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.60% | | | |
Mortgages and other indebtedness | | | | | | | $ 7,929,000 | | | 7,994,000 |
Harrodsburg Marketplace | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 19,112 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.55% | | | |
Mortgages and other indebtedness | | | | | | | $ 3,520,000 | | | 3,553,000 |
Graystone Crossing | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 20,386 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.55% | | | |
Mortgages and other indebtedness | | | | | | | $ 3,896,000 | | | 3,928,000 |
Bryan Station | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 23,489 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.52% | | | |
Mortgages and other indebtedness | | | | | | | $ 4,510,000 | | | 4,547,000 |
Crockett Square | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.47% | | | |
Mortgages and other indebtedness | | | | | | | $ 6,338,000 | | | 6,338,000 |
Pierpont Centre | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.15% | | | |
Mortgages and other indebtedness | | | | | | | $ 8,113,000 | | | 8,113,000 |
Alex City Marketplace | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 3.95% | | | |
Mortgages and other indebtedness | | | | | | | $ 5,750,000 | | | 5,750,000 |
Butler Square | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 3.90% | | | |
Mortgages and other indebtedness | | | | | | | $ 5,640,000 | | | 5,640,000 |
Brook Run Shopping Center | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.08% | | | |
Mortgages and other indebtedness | | | | | | | $ 10,950,000 | | | 10,950,000 |
Beaver Ruin Village I and II | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.73% | | | |
Mortgages and other indebtedness | | | | | | | $ 9,400,000 | | | 9,400,000 |
Sunshine Shopping Plaza | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.57% | | | |
Mortgages and other indebtedness | | | | | | | $ 5,900,000 | | | 5,900,000 |
Barnett Portfolio | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.30% | | | |
Mortgages and other indebtedness | | | | | | | $ 8,770,000 | | | 8,770,000 |
Fort Howard Shopping Center | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.57% | | | |
Mortgages and other indebtedness | | | | | | | $ 7,100,000 | | | 7,100,000 |
Conyers Crossing | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.67% | | | |
Mortgages and other indebtedness | | | | | | | $ 5,960,000 | | | 5,960,000 |
Grove Park Shopping Center | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.52% | | | |
Mortgages and other indebtedness | | | | | | | $ 3,800,000 | | | 3,800,000 |
Parkway Plaza | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.57% | | | |
Mortgages and other indebtedness | | | | | | | $ 3,500,000 | | | 3,500,000 |
Winslow Plaza | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.82% | | | |
Mortgages and other indebtedness | | | | | | | $ 4,620,000 | | | 4,620,000 |
JANAF BJ's | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 29,964 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.95% | | | |
Mortgages and other indebtedness | | | | | | | $ 5,117,000 | | | 0 |
Chesapeake Square | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | $ 23,857 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.70% | | | |
Mortgages and other indebtedness | | | | | | | $ 4,468,000 | | | 4,507,000 |
Berkley/Sangaree/Tri-County | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.78% | | | |
Mortgages and other indebtedness | | | | | | | $ 9,400,000 | | | 9,400,000 |
Riverbridge | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.48% | | | |
Mortgages and other indebtedness | | | | | | | $ 4,000,000 | | | 4,000,000 |
Franklin | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 4.93% | | | |
Mortgages and other indebtedness | | | | | | | $ 8,516,000 | | | 8,516,000 |
Revere Loan | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | $ 150,000 | $ 2,600,000 | | | | | $ 100,000 | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 9.00% | 9.00% | 8.00% | |
Mortgages and other indebtedness | | | | | | | $ 3,358,000 | $ 3,500,000 | $ 6,810,000 | 6,808,000 |
Line of Credit | Monarch Bank Line Of Credit | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, periodic payment | | | | | | | 24,656 | | | |
Mortgages and other indebtedness | | | | | | | $ 3,000,000 | | | 3,000,000 |
Line of Credit | Monarch Bank Line Of Credit | LIBOR | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, basis spread on variable rate | | | | | | | 3.50% | | | |
Line of Credit | KeyBank Line of Credit | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Mortgages and other indebtedness | | | | | | | $ 6,402,000 | | | 15,532,000 |
Line of Credit | KeyBank Line of Credit | LIBOR | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, basis spread on variable rate | | | | | | | 2.50% | | | |
Line of Credit | KeyBank Line of Credit Maturing December 2019 | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Mortgages and other indebtedness | | | | | | | $ 52,500,000 | | | 52,500,000 |
Line of Credit | KeyBank Line of Credit Maturing December 2019 | LIBOR | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, basis spread on variable rate | | | | | | | 2.50% | | | |
Senior convertible notes | Senior convertible notes | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | |
Debt instrument, payment terms | | | | | | | Interest only | | | |
Debt instrument, interest rate. stated percentage | | | | | | | 9.00% | | | |
Mortgages and other indebtedness | | | | | | | $ 1,369,000 | | | $ 1,369,000 |