v3.8.0.1

Unsecured Credit Agreements - Additional Information (Detail) |  |  | 12 Months Ended |
--- | --- | --- | --- | ---
Jun. 23, 2017 USD ($) Bank Option | Apr. 18, 2017 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Nov. 20, 2017 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |
Repayment of line of credit |  |  | $ 323,000,000 | $ 206,500,000 | $ 408,500,000 |
Additional borrowing capacity |  |  |  |  |  | $ 80,000,000
Revolving credit facility, available borrowing capacity |  |  |  |  |  | 880,000,000
One time non pro rata paydown amount | $ 50,000,000 |  |  |  |  |
Weighted average interest rate on all outstanding borrowings |  |  | 3.03% | 2.14% |  |
Amortization of debt issuance costs charged to interest expense |  |  | $ 1,893,000 | $ 1,626,000 | 1,181,000 |
Interest Expense |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Amortization of debt issuance costs charged to interest expense |  |  | 1,794,000 | $ 1,817,000 | $ 1,321,000 |
Other Income (Expenses) - Cost of Debt Extinguishment |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Amortization of debt issuance costs charged to interest expense |  |  | 2,901,000 |  |  |
Unamortized debt issuance costs |  |  | 654,000 |  |  |
Other Income (Expenses) - Cost of Debt Extinguishment | Senior Notes |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Amortization of debt issuance costs charged to interest expense |  |  | $ 8,711,000 |  |  |
Minimum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt instrument, term |  |  | 59 months |  |  |
Maximum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt instrument, term |  |  | 239 months |  |  |
Revolver | Baa3 Rating |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Basis spread on variable rate | 1.20% |  |  |  |  |
5.5 Year Term Loan |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt instrument, face amount |  |  |  |  |  | 265,000,000
Commitment fee percentage | 0.25% |  |  |  |  |
5.5 Year Term Loan | Baa3 Rating |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Basis spread on variable rate | 1.35% |  |  |  |  |
7 Year Term Loan |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt instrument, face amount |  |  |  |  |  | 190,000,000
Commitment fee percentage | 0.25% |  |  |  |  |
7 Year Term Loan | Baa3 Rating |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Basis spread on variable rate | 1.90% |  |  |  |  |
Unsecured Revolving Credit Facility | M&T and Regions Bank |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Repayment of line of credit | $ 5,000,000 |  |  |  |  |
Unsecured Term Note | Regions Bank |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Repayment of unsecured long-term debt | 185,000,000 |  |  |  |  |
Unsecured Term Note | Sun Trust Bank |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Repayment of unsecured long-term debt | 50,000,000 |  |  |  |  |
Unsecured Term Note | M&T and Regions Bank |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Repayment of unsecured long-term debt | 100,000,000 |  |  |  |  |
Revolver |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt instrument, face amount |  |  |  |  |  | $ 425,000,000
2017 Unsecured Revolving Credit and Term Loan Agreement |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt instrument, face amount | $ 800,000,000 |  |  |  |  |
Number of participating banks as joint lead arrangers and joint bookrunners | Bank | 4 |  |  |  |  |
Number of participating banks as co-syndication agents | Bank | 4 |  |  |  |  |
Number of participating banks as co-documentation agents | Bank | 4 |  |  |  |  |
Line of credit, maximum accordion feature | $ 1,000,000,000 |  |  |  |  |
2017 Unsecured Revolving Credit and Term Loan Agreement | Revolver |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Line of credit, maximum borrowing capacity | 400,000,000 |  |  |  |  |
Sublimit for swingline loans | 35,000,000 |  |  |  |  |
Amount available for issuance of letters of credit | $ 20,000,000 |  |  |  |  |
Maturity date | Jan. 31, 2022 |  |  |  |  |
Number of option available to extend maturity period | Option | 1 |  |  |  |  |
Maturity extension period | 5 months |  |  |  |  |
Maturity extension fee percentage | 0.0625% |  |  |  |  |
Commitment fee percentage | 0.25% |  |  |  |  |
2017 Unsecured Revolving Credit and Term Loan Agreement | Revolver | LIBOR | Minimum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Basis spread on variable rate | 0.825% |  |  |  |  |
2017 Unsecured Revolving Credit and Term Loan Agreement | Revolver | LIBOR | Maximum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Basis spread on variable rate | 1.55% |  |  |  |  |
2017 Unsecured Revolving Credit and Term Loan Agreement | 5.5 Year Term Loan |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt instrument, face amount | $ 250,000,000 |  |  |  |  |
Debt instrument, term | 5 years 6 months |  |  |  |  |
Maturity date | Jan. 31, 2023 |  |  |  |  |
2017 Unsecured Revolving Credit and Term Loan Agreement | 5.5 Year Term Loan | LIBOR | Minimum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Basis spread on variable rate | 0.90% |  |  |  |  |
2017 Unsecured Revolving Credit and Term Loan Agreement | 5.5 Year Term Loan | LIBOR | Maximum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Basis spread on variable rate | 1.75% |  |  |  |  |
2017 Unsecured Revolving Credit and Term Loan Agreement | 7 Year Term Loan |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt instrument, face amount | $ 150,000,000 |  |  |  |  |
Debt instrument, term | 7 years |  |  |  |  |
Maturity date | Jun. 30, 2024 |  |  |  |  |
2017 Unsecured Revolving Credit and Term Loan Agreement | 7 Year Term Loan | LIBOR | Minimum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Basis spread on variable rate | 1.50% |  |  |  |  |
2017 Unsecured Revolving Credit and Term Loan Agreement | 7 Year Term Loan | LIBOR | Maximum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Basis spread on variable rate | 2.45% |  |  |  |  |
2015 Unsecured Term Loan Agreement |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Maturity date | Feb. 28, 2019 |  |  |  |  |
Number of option available to extend maturity period | Option | 2 |  |  |  |  |
Maturity extension period | 1 year |  |  |  |  |
Maturity extension fee percentage | 0.01% |  |  |  |  |
2015 Unsecured Term Loan Agreement | Baa3 Rating |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Basis spread on variable rate | 1.40% |  |  |  |  |
2015 Unsecured Term Loan Agreement | 1 Month LIBOR | Minimum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Basis spread on variable rate | 0.90% |  |  |  |  |
2015 Unsecured Term Loan Agreement | 1 Month LIBOR | Maximum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Basis spread on variable rate | 1.75% |  |  |  |  |
2017 Senior Notes |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt instrument, term |  |  | 10 years |  |  |
Maturity date |  |  | Apr. 18, 2017 |  |  |
Proceeds from issuance of debt |  | $ 150,000,000 |  |  |  |
Debt instrument, interest rate |  | 4.84% |  |  |  |
Issuance date |  |  | Apr. 18, 2027 |  |  |
2017 Senior Notes | Other Income (Expenses) - Cost of Debt Extinguishment |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Amortization of debt issuance costs charged to interest expense |  |  | $ 5,810,000 |  |  |
2017 Senior Notes | 10-Year U.S. Treasury Yield |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt instrument basis spread on reference rate |  | 2.40% |  |  |  |

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