Interest Rate Swaps - Summary of Interest Rate Swap Agreements (Detail) - USD ($)	3 Months Ended
Sep. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Principal amount	$ 666,979,000	$ 502,476,000
Fair Value	785,000	2,045,000
Interest Rate Swap 1
Derivative [Line Items]
Fair Value	$ 0
Derivative Financial Instruments, Assets \| Interest Rate Swap 1
Derivative [Line Items]
Interest rate swap agreement, effective date	Feb. 14, 2018
Interest rate swap agreement, maturity date	Jan. 14, 2022
Interest Strike Rate	1.349%
Fair Value	$ 2,521,000	3,245,000
Current Notional Value	$ 0	0
Derivative Financial Instruments, Assets \| Interest Rate Swap 2
Derivative [Line Items]
Interest rate swap agreement, effective date	Aug. 14, 2018
Interest rate swap agreement, maturity date	Jan. 14, 2022
Interest Strike Rate	1.406%
Fair Value	$ 1,763,000	2,349,000
Current Notional Value	$ 0	0
Derivative Financial Instruments, Assets \| Interest Rate Swap 7
Derivative [Line Items]
Interest rate swap agreement, effective date	Dec. 14, 2018
Interest rate swap agreement, maturity date	Aug. 14, 2021
Interest Strike Rate	1.764%
Fair Value	$ 468,000	0
Current Notional Value	$ 0	0
Derivative Financial Instruments, Assets \| Interest Rate Swap 5
Derivative [Line Items]
Interest Strike Rate	1.8975%
Derivative Financial Instruments, Liabilities
Derivative [Line Items]
Current Notional Value	$ 50,000,000
Derivative Financial Instruments, Liabilities \| Interest Rate Swap 3
Derivative [Line Items]
Interest rate swap agreement, effective date	Jan. 15, 2015
Interest rate swap agreement, maturity date	Feb. 15, 2019
Interest Strike Rate	1.826%
Fair Value	$ 121,000	338,000
Current Notional Value	$ 30,000,000	30,000,000
Derivative Financial Instruments, Liabilities \| Interest Rate Swap 4
Derivative [Line Items]
Interest rate swap agreement, effective date	Jul. 15, 2015
Interest rate swap agreement, maturity date	Feb. 15, 2019
Interest Strike Rate	2.01%
Fair Value	$ 187,000	440,000
Current Notional Value	$ 29,087,000	29,674,000
Derivative Financial Instruments, Liabilities \| Interest Rate Swap 5
Derivative [Line Items]
Interest rate swap agreement, effective date	Aug. 14, 2015
Interest rate swap agreement, maturity date	Dec. 14, 2018
Interest Strike Rate	1.79%
Fair Value	$ 174,000	529,000
Current Notional Value	$ 50,000,000	50,000,000
Derivative Financial Instruments, Liabilities \| Interest Rate Swap 6
Derivative [Line Items]
Interest rate swap agreement, effective date	Feb. 16, 2016
Interest rate swap agreement, maturity date	Dec. 14, 2018
Interest Strike Rate	2.005%
Fair Value	$ 303,000	738,000
Current Notional Value	50,000,000	50,000,000
$100M Term Loan Facility \| LIBOR
Derivative [Line Items]
Principal amount	$ 100,000,000	$ 100,000,000

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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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

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Fixed interest rate related to the interest rate derivative.

+ References

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- Definition

Date the entity entered into the derivative contract, in CCYY-MM-DD format.

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Date the derivative contract matures, in CCYY-MM-DD format.

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- Definition

Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

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