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Indebtedness Schedule of Long-Term Debt (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
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Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] |  |
Schedule of Debt Instruments [Line Items] |  |
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net | $ 0 |
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate | 3.03% |
Long-term Debt, Gross | $ 60,000 |
Long-term Debt | 60,000 | $ 60,000
One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member] |  |
Schedule of Debt Instruments [Line Items] |  |
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net | $ 0 |
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate | 1.56% |
Long-term Debt, Gross | $ 25,000 |
Long-term Debt | 25,000 | 25,000
One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] |  |
Schedule of Debt Instruments [Line Items] |  |
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net | $ 0 |
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate | 1.61% |
Long-term Debt, Gross | $ 25,000 |
Long-term Debt | 25,000 | 25,000
Five Point Eight Hundred Seventy Five Percent Senior Notes [Member] |  |
Schedule of Debt Instruments [Line Items] |  |
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net | $ (4,570) |
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate | 5.88% |
Long-term Debt, Gross | $ 185,000 |
Long-term Debt | 180,430 | 180,068
Six Point Seventy Percent Senior Notes [Member] |  |
Schedule of Debt Instruments [Line Items] |  |
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net | $ (989) |
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate | 6.70% |
Long-term Debt, Gross | $ 100,000 |
Long-term Debt | 99,011 | 98,952
Seven Point Twenty Five Percent Senior Notes [Member] |  |
Schedule of Debt Instruments [Line Items] |  |
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net | $ (325) |
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate | 7.25% |
Long-term Debt, Gross | $ 50,000 |
Long-term Debt | 49,675 | 49,647
Long-term Debt [Member] |  |
Schedule of Debt Instruments [Line Items] |  |
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net | (5,884) |
Long-term Debt, Gross | 445,000 |
Long-term Debt | $ 439,116 | $ 438,667

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- Definition [Line Items] for Schedule of Debt Instruments [Table] + References No definition available. + Details
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- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. + 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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- Definition Amount of unamortized debt discount (premium) and debt issuance costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399 + Details
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- Definition The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate. + 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(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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