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Unsecured Credit Facility (Details) $ in Thousands |  | 12 Months Ended |  |
--- | --- | --- | --- | ---
Apr. 24, 2017 USD ($) mo | Dec. 31, 2017 USD ($) | Dec. 31, 2017 USD ($) yr | Apr. 23, 2017 USD ($) | Dec. 31, 2016 USD ($)
Line of Credit Facility [Line Items] |  |  |  |  |
Line of Credit Facility, Amount Outstanding |  | $ 45,000 | $ 45,000 |  | $ 0
Revolving Credit Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity | $ 1,500,000 |  |  | $ 1,000,000 |
Competitive bid quote | 65.00% |  |  |  |
Maximum Leverage Ratio |  | 60.00% |  |  |
Leverage Ratio Maximum Increasing Limit |  | 65.00% |  |  |
Leverage Ratio Reduction Limit |  | 60.00% |  |  |
Leverage Ratio Reduction Period, Years | yr |  |  | 1 |  |
Maximum Secured Debt Leverage Ratio |  | 55.00% |  |  |
Fixed Charge Coverage Ratio Minimum. |  | 1.40 | 1.40 |  |
Maximum Unsecured Debt Leverage Ratio |  | 60.00% |  |  |
Unsecured Debt Leverage Ratio Maximum Increasing Limit |  | 65.00% |  |  |
Unsecured Debt Leverage Ratio Reduction Limit |  | 60.00% |  |  |
Unsecured Debt Leverage Ratio Reduction Period, Years |  | 1.75 | 1 |  |
Delayed Draw Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity | $ 500,000 |  |  | $ 500,000 |
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage | 0.15% |  |  |  |
Line of Credit Facility, Frequency of Commitment Fee Payment | 4 |  |  |  |
minimum borrowing amount | $ 50,000 |  |  |  |
Maximum [Member] | Revolving Credit Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage | 0.30% |  |  |  |
Minimum [Member] | Revolving Credit Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage | 0.10% |  |  |  |
Current credit rating [Member] | Revolving Credit Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage |  | 0.15% |  |  |
Interest Rate Based on LIBOR or CDOR [Member] | Maximum [Member] | Revolving Credit Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Margin added to Calculated Interest Rate | 1.55% |  |  |  |
Interest Rate Based on LIBOR or CDOR [Member] | Maximum [Member] | Delayed Draw Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Margin added to Calculated Interest Rate | 1.75% |  |  |  |
Interest Rate Based on LIBOR or CDOR [Member] | Minimum [Member] | Revolving Credit Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Margin added to Calculated Interest Rate | 0.775% |  |  |  |
Interest Rate Based on LIBOR or CDOR [Member] | Minimum [Member] | Delayed Draw Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Margin added to Calculated Interest Rate | 0.85% |  |  |  |
Interest Rate Based on LIBOR or CDOR [Member] | Current credit rating [Member] | Revolving Credit Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Margin added to Calculated Interest Rate |  | 0.875% | 0.875% |  |
Interest Rate Based on LIBOR or CDOR [Member] | Current credit rating [Member] | Delayed Draw Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Margin added to Calculated Interest Rate |  | 0.95% | 0.95% |  |
Alternative Base Interest Rate Calculation [Member] | Revolving Credit Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Amount added to Federal Funds Rate to Calculate Interest Rate | 0.50% |  |  |  |
LIBOR Period Used to Calculate Interest Rate (in months) | mo | 1 |  |  |  |
Amount added to LIBOR to Calculate Interest Rate | 1.00% |  |  |  |
Alternative Base Interest Rate Calculation [Member] | Maximum [Member] | Revolving Credit Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Margin added to Calculated Interest Rate | 0.55% |  |  |  |
Alternative Base Interest Rate Calculation [Member] | Maximum [Member] | Delayed Draw Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Margin added to Calculated Interest Rate | 0.75% |  |  |  |
Alternative Base Interest Rate Calculation [Member] | Minimum [Member] | Revolving Credit Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Margin added to Calculated Interest Rate | 0.00% |  |  |  |
Alternative Base Interest Rate Calculation [Member] | Minimum [Member] | Delayed Draw Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Margin added to Calculated Interest Rate | 0.00% |  |  |  |
Alternative Base Interest Rate Calculation [Member] | Current credit rating [Member] | Revolving Credit Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Margin added to Calculated Interest Rate |  | 0.00% | 0.00% |  |
Alternative Base Interest Rate Calculation [Member] | Current credit rating [Member] | Delayed Draw Facility [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Margin added to Calculated Interest Rate |  | 0.00% | 0.00% |  |

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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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- Definition Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility. + 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 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Description of when the fee for available but unused credit capacity is required to be paid (for example, annually, quarterly, or monthly). + 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 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility. + References No definition available. + Details
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