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v3.8.0.1

Line of Credit, Long-Term Debt and Capital Lease Obligations - Additional Information (Detail) - USD ($) | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 08, 2015
Debt Instrument [Line Items] |  |  |
Line of Credit facility, maturity date | Oct. 31, 2022 |  |
Long term debt | $ 1,846,133,000 | $ 1,698,744,000 |
Letters of credit outstanding amount | 200,000 |  |
Line of Credit facility, available balance | $ 889,300,000 |  |
Minimum [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Commitment fee percentage | 0.15% |  |
Maximum [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Commitment fee percentage | 0.30% |  |
Alternate Base Rate [Member] | Federal Funds Rate [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument, interest rate | Federal Funds Rate plus 1/2 of 1.00% |  |
Alternate Base Rate [Member] | LIBOR [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument, interest rate | LIBOR for an interest period of one month plus 1.00% |  |
Debt instrument, variable interest rate | 1.00% |  |
Applicable Margin Rate [Member] | LIBOR [Member] | Minimum [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument, variable interest rate | 0.125% |  |
Applicable Margin Rate [Member] | LIBOR [Member] | Maximum [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument, variable interest rate | 0.75% |  |
Unsecured Revolving Credit Facility [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Line of Credit facility, borrowing capacity | $ 2,000,000,000 |  |
Letters of Credit [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Line of Credit facility, borrowing capacity | $ 37,500,000 |  |
5.25% Senior Unsecured Notes Due 2023 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Aggregate principal amount of debt |  |  | $ 750,000,000
Debt instrument interest rate |  |  | 5.25%
Debt instrument maturity date description | Payable semi-annually in arrears on June 1 and December 1 |  |
Debt instrument, maturity year | 2023 |  |
Long term debt | $ 740,497,000 | 738,891,000 |
Estimated fair value of notes | $ 763,100,000 | $ 773,400,000 |
5.25% Senior Unsecured Notes Due 2023 [Member] | Change In Control [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Redemption percentage of principal amount | 101.00% |  |
5.25% Senior Unsecured Notes Due 2023 [Member] | Redemption Before 2018 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Redemption percentage of principal amount | 100.00% |  |
5.25% Senior Unsecured Notes Due 2023 [Member] | Redemption Before 2018 [Member] | Redeem up to 35% of Aggregate Principal Amount [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Redemption percentage of principal amount | 35.00% |  |
Redemption price percentage of aggregate principal amount redeemed | 105.25% |  |
5.25% Senior Unsecured Notes Due 2023 [Member] | Redemption in 2018 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Redemption percentage of principal amount | 103.938% |  |
5.25% Senior Unsecured Notes Due 2023 [Member] | Redemption in 2019[Member] |  |  |
Debt Instrument [Line Items] |  |  |
Redemption percentage of principal amount | 102.625% |  |
5.25% Senior Unsecured Notes Due 2023 [Member] | Redemption in 2020 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Redemption percentage of principal amount | 101.313% |  |
5.25% Senior Unsecured Notes Due 2023 [Member] | Redemption in 2021 and Thereafter [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Redemption percentage of principal amount | 100.00% |  |

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