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Notes Payable (Narrative) (Details) |  | 12 Months Ended |  |
--- | --- | --- | --- | ---
Jul. 02, 2013 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 03, 2015 USD ($)
Debt Instrument [Line Items] |  |  |  |
Loan maximum borrowing capacity | $ 250,000,000 |  |  |
Revolving credit facility term | 5 years |  |  |
Unsecured credit facility |  | $ 180,000,000 |  |
Minimum [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Advance rate used to calculate collateral requirement |  | 75.00% |  |
Maximum [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Advance rate used to calculate collateral requirement |  | 100.00% |  |
Bank Of America [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Basis spread on variable rate |  | 0.40% |  |
Secured debt, other |  | $ 20,000,000 |  |
AIS [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Secured debt, other |  | $ 120,000,000 |  |
Revolving Credit Facility [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Loan maximum borrowing capacity | $ 200,000,000 |  | $ 250,000,000 | $ 250,000,000
Revolving credit facility term | 5 years |  |  |
Commitment fee on undrawn portion of facility |  | 0.125% |  |
Unsecured credit facility |  | $ 180,000,000 |  |
Interest rate at period end |  | 1.73% |  |
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% |  |  |
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% |  |  |
Revolving Credit Facility [Member] | LIBOR [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Basis spread on variable rate |  | 1.125% |  |
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 |  |  |
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 |  |  |

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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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