Debt - Additional Information (Details) | Nov. 07, 2017USD ($) | Feb. 10, 2017USD ($)Agreement | Feb. 09, 2017USD ($) | Sep. 30, 2017USD ($) | Sep. 30, 2016USD ($) | Sep. 30, 2017USD ($) | Sep. 30, 2016USD ($) | Dec. 31, 2016USD ($) | May 31, 2016USD ($) |
Debt Instrument [Line Items] | | | | | | | | | |
Line of credit facility maximum borrowing capacity | | | $ 300,000,000 | $ 260,800,000 | | $ 260,800,000 | | | |
Line of credit facility maturity date | | | 2017-11 | | | | | | |
Commitment fees paid | | $ 2,700,000 | | | | | | | |
Debt instrument description | | | | | | The revolving credit facility has one 12-month extension option, subject to certain conditions, including the payment of a 0.15% extension fee. | | | |
Debt instrument, extension fee | | | | | | 0.15% | | | |
Debt instrument collateral amount | | 1,000,000,000 | | | | | | | |
Line of credit facility minimum borrowing base | | $ 500,000,000 | | | | | | | |
Unamortized deferred financing costs | | | | 718,000 | | $ 718,000 | | | |
Number of interest rate swap agreements | Agreement | | 4 | | | | | | | |
Interest rate swap agreement effective date | | Apr. 10, 2017 | | | | | | | |
Estimated additional reclassification from other comprehensive income (loss) to interest expense | | | | | | 500,000 | | | |
Fair value interest rate swap on net liability position including accrued interest but excluding adjustment for nonperformance risk | | | | 100,000 | | 100,000 | | | |
Provisions breached to settle under agreement at aggregate termination value | | | | 100,000 | | 100,000 | | | |
Subsequent Event | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Line of credit facility outstanding amount | $ 207,500,000 | | | | | | | | |
Maximum | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Line of credit facility leverage ratio | | 50.00% | | | | | | | |
Maximum | Interest Rate Swap Agreements | Accounts Payable And Accrued Liabilities | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Fair value of derivative financial instruments | | | | 100,000 | | 100,000 | | | |
LIBOR | Minimum [Member] | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Debt instrument interest rate | | 1.75% | 2.75% | | | | | | |
LIBOR | Maximum | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Debt instrument interest rate | | 3.00% | 3.75% | | | | | | |
Base Rate | Minimum [Member] | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Debt instrument interest rate | | 0.75% | 2.00% | | | | | | |
Base Rate | Maximum | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Debt instrument interest rate | | 2.00% | 2.50% | | | | | | |
Term Loan | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Line of credit facility maximum borrowing capacity | | $ 125,000,000 | | | | | | | |
Line of credit facility maturity date | | 2022-02 | | | | | | | |
Commitment fees paid | | $ 800,000 | | | | | | | |
Deferred financing costs, gross | | | | 800,000 | | 800,000 | | | |
Debt financing costs, net | | | | $ 700,000 | | $ 700,000 | | | |
Term Loan | Subsequent Event | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Line of credit facility outstanding amount | $ 125,000,000 | | | | | | | | |
Accordion Feature Debt | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Line of credit facility maximum borrowing capacity | | 700,000,000 | | | | | | | |
Secured Revolving Credit facility | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Line of credit facility maximum borrowing capacity | | $ 300,000,000 | | | | | | | |
Line of credit facility maturity date | | 2021-02 | | | | | | | |
Commitment fees paid | | $ 1,900,000 | | | | | | | |
Debt instrument, weighted average interest | | | | 3.40% | 3.80% | 3.40% | 3.80% | | |
Costs related to revolving credit facility, gross | | | | $ 3,300,000 | | $ 3,300,000 | | | |
Costs related to revolving credit facility, net | | | | 2,800,000 | | 2,800,000 | | | |
Amortization expense of deferred financing costs | | | | 200,000 | $ 400,000 | 800,000 | $ 2,000,000 | | |
Unamortized deferred financing costs | | | | | | | | | $ 300,000 |
Line of credit facility outstanding amount | | | | $ 82,500,000 | | $ 82,500,000 | | $ 144,000,000 | |
Secured Revolving Credit facility | Subsequent Event | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Debt instrument, weighted average interest | 2.99% | | | | | | | | |
Line of credit facility outstanding amount | $ 82,500,000 | | | | | | | | |
Line of credit facility additional borrowing capacity | $ 53,300,000 | | | | | | | | |
Secured Revolving Credit facility | Minimum [Member] | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Line of credit facility unused fees | | | | | | 0.25% | | | |
Line of credit facility usage fees | | | | | | 50.00% | | | |
Secured Revolving Credit facility | Maximum | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Line of credit facility unused fees | | | | | | 0.35% | | | |
Line of credit facility usage fees | | | | | | 50.00% | | | |
Secured Revolving Credit facility | LIBOR | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Debt instrument interest rate | | 1.84% | | | | | | | |
Secured Revolving Credit facility | LIBOR | Subsequent Event | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | |
Debt instrument interest rate | 1.75% | | | | | | | | |