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Notes Payable (Narrative) (Details) |  |  | 6 Months Ended |
--- | --- | --- | --- | ---
Mar. 29, 2017 USD ($) | Mar. 08, 2017 USD ($) | Jun. 30, 2017 USD ($) | Dec. 31, 2016 USD ($)
Debt Instrument [Line Items] |  |  |  |
Less unamortized discount and debt issuance costs |  |  | $ 3,864,000 | $ 0
Document Period End Date |  |  | Jun. 30, 2017 |
Unsecured debt [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Gross proceeds from issuance of senior notes |  | $ 375,000,000 |  |
Interest rate |  | 4.40% |  |
Debt issuance cost |  | $ 3,400,000 |  |
Debt instrument, discount percent |  | 99.847% |  |
Effective interest rate |  | 4.45% |  |
Secured Notes Two [Member] | Revolving Credit Facility [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Loan maximum borrowing capacity | $ 50,000,000 |  |  |
Revolving credit facility term | 5 years |  |  |
Secured Notes Two [Member] | Revolving Credit Facility [Member] | Minimum [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt to total capital ratio | 0.15 |  |  |
Commitment fee on undrawn portion of facility | 0.125% |  | 0.15% |
Secured Notes Two [Member] | Revolving Credit Facility [Member] | Maximum [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt to total capital ratio | 0.25 |  |  |
Commitment fee on undrawn portion of facility | 0.225% |  |  |
Secured Notes Two [Member] | Revolving Credit Facility [Member] | LIBOR [Member] | Minimum [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Basis spread on variable rate | 1.125% |  |  |
Debt to total capital ratio | 0.15 |  |  |
Secured Notes Two [Member] | Revolving Credit Facility [Member] | LIBOR [Member] | Maximum [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Basis spread on variable rate | 1.625% |  |  |
Debt to total capital ratio | 0.25 |  |  |
Unsecured Notes Three [Member] | Revolving Credit Facility [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Loan maximum borrowing capacity | $ 50,000,000 |  |  |
Revolving credit facility term | 5 years |  |  |
Unamortized debt issuance cost | $ 200,000 |  |  |
Unsecured Notes Three [Member] | Revolving Credit Facility [Member] | Maximum [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt to total capital ratio |  |  | 0.175 |
Level 2 [Member] | Secured Notes Two [Member] | LIBOR [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Basis spread on variable rate |  |  | 0.40% |
Level 2 [Member] | Borrowings [Member] | Unsecured Notes Two [Member] | Unsecured debt [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Unsecured debt |  | $ 375,000,000 | $ 375,000,000 | $ 0
Interest rate |  |  | 4.40% |
Less unamortized discount and debt issuance costs |  |  | $ 3,900,000 |
Level 2 [Member] | Borrowings [Member] | Unsecured Notes Three [Member] | Unsecured debt [Member] | LIBOR [Member] | Minimum [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Basis spread on variable rate |  |  | 0.1125% |
Level 2 [Member] | Borrowings [Member] | Unsecured Notes Three [Member] | Unsecured debt [Member] | LIBOR [Member] | Maximum [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Basis spread on variable rate |  |  | 0.1625% |

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- Definition The end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented. If there is no historical data in the report, use the filing date. The format of the date is CCYY-MM-DD. + References No definition available. + Details
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