v3.8.0.1

Interest Rate Swaps - Summary of Interest-rate Swap Agreements (Detail) - Interest Rate Swap - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Fair Value	$ 5,988,000	$ (619,000)
Bank of America
Derivative [Line Items]
Derivative, Maturity date	Nov. 30, 2023
Derivative, Fixed rate	2.80%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value	$ (863,000)	(1,338,000)
Bank of Montreal One
Derivative [Line Items]
Derivative, Maturity date	Jul. 31, 2024
Derivative, Fixed rate	1.16%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 40,000,000
Fair Value	$ 2,503,000	2,485,000
Bank of Montreal Two
Derivative [Line Items]
Derivative, Maturity date	Jan. 31, 2025
Derivative, Fixed rate	1.91%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value	$ 464,000	299,000
Bank of Montreal Three
Derivative [Line Items]
Derivative, Maturity date	Jul. 31, 2025
Derivative, Fixed rate	2.32%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value	$ (194,000)	(433,000)
Bank of Montreal Four
Derivative [Line Items]
Derivative, Maturity date	Jan. 31, 2026
Derivative, Fixed rate	1.92%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value	$ 561,000	437,000
Bank of Montreal Five
Derivative [Line Items]
Derivative, Maturity date	Jan. 31, 2026
Derivative, Fixed rate	2.05%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 40,000,000
Fair Value	$ 520,000	275,000
Bank of Montreal Six
Derivative [Line Items]
Derivative, Maturity date	Dec. 31, 2026
Derivative, Fixed rate	2.33%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 10,000,000
Fair Value	$ (63,000)	(132,000)
Bank of Montreal Seven
Derivative [Line Items]
Derivative, Maturity date	Dec. 31, 2027
Derivative, Fixed rate	2.37%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value	$ (192,000)
Capital One One
Derivative [Line Items]
Derivative, Maturity date	Dec. 31, 2021
Derivative, Fixed rate	1.05%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 15,000,000
Fair Value	$ 607,000	552,000
Capital One Two
Derivative [Line Items]
Derivative, Maturity date	Dec. 31, 2024
Derivative, Fixed rate	1.58%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 15,000,000
Fair Value	$ 603,000	565,000
Capital One Three
Derivative [Line Items]
Derivative, Maturity date	Jan. 31, 2026
Derivative, Fixed rate	2.08%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 35,000,000
Fair Value	$ 399,000	216,000
Capital One Four
Derivative [Line Items]
Derivative, Maturity date	Jul. 31, 2026
Derivative, Fixed rate	1.32%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 35,000,000
Fair Value	$ 2,565,000	2,667,000
Capital One Five
Derivative [Line Items]
Derivative, Maturity date	Dec. 31, 2027
Derivative, Fixed rate	2.37%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value	$ (189,000)
M&T Bank
Derivative [Line Items]
Derivative, Maturity date	Sep. 30, 2017
Derivative, Fixed rate	1.09%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value		(37,000)
M&T Bank One
Derivative [Line Items]
Derivative, Maturity date	Apr. 30, 2020
Derivative, Fixed rate	4.91%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 21,335,000
Fair Value		(2,266,000)
M&T Bank Two
Derivative [Line Items]
Derivative, Maturity date	Aug. 31, 2021
Derivative, Fixed rate	1.02%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 5,183,000
Fair Value	$ 182,000
M&T Bank Three
Derivative [Line Items]
Derivative, Maturity date	Sep. 30, 2022
Derivative, Fixed rate	2.83%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value	$ (810,000)	(993,000)
M&T Bank Four
Derivative [Line Items]
Derivative, Maturity date	Nov. 30, 2023
Derivative, Fixed rate	2.65%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value	$ (686,000)	(1,102,000)
Regions Bank
Derivative [Line Items]
Derivative, Maturity date	Mar. 31, 2017
Derivative, Fixed rate	0.70%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 50,000,000
Fair Value		6,000
Regions Bank One
Derivative [Line Items]
Derivative, Maturity date	Mar. 31, 2018
Derivative, Fixed rate	1.77%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value	$ (9,000)	(179,000)
Regions Bank Two
Derivative [Line Items]
Derivative, Maturity date	Mar. 31, 2019
Derivative, Fixed rate	1.91%
Variable Rate Index	LIBOR 3 month
Notional Amount	$ 25,000,000
Fair Value	$ 2,000	(239,000)
Regions Bank Three
Derivative [Line Items]
Derivative, Maturity date	May 31, 2020
Derivative, Fixed rate	2.12%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 50,000,000
Fair Value	$ (153,000)	(940,000)
Regions Bank Four
Derivative [Line Items]
Derivative, Maturity date	Mar. 31, 2022
Derivative, Fixed rate	2.43%
Variable Rate Index	LIBOR 3 month
Notional Amount	$ 25,000,000
Fair Value	$ (254,000)	(594,000)
Regions Bank Five
Derivative [Line Items]
Derivative, Maturity date	Dec. 31, 2023
Derivative, Fixed rate	1.18%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value	$ 1,402,000	1,392,000
Sun Trust Bank One
Derivative [Line Items]
Derivative, Maturity date	Apr. 30, 2024
Derivative, Fixed rate	1.99%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value	$ 261,000	47,000
Sun Trust Bank Two
Derivative [Line Items]
Derivative, Maturity date	Apr. 30, 2025
Derivative, Fixed rate	2.20%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value		(219,000)
Sun Trust Bank Three
Derivative [Line Items]
Derivative, Maturity date	Jul. 31, 2025
Derivative, Fixed rate	1.99%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value	$ 386,000	228,000
Sun Trust Bank Four
Derivative [Line Items]
Derivative, Maturity date	Dec. 31, 2025
Derivative, Fixed rate	2.30%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value	$ (138,000)
Sun Trust Bank Five
Derivative [Line Items]
Derivative, Maturity date	Jan. 31, 2026
Derivative, Fixed rate	1.93%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 25,000,000
Fair Value	$ 553,000	429,000
Wells Fargo Bank One
Derivative [Line Items]
Derivative, Maturity date	Feb. 28, 2021
Derivative, Fixed rate	2.39%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 35,000,000
Fair Value	$ (369,000)	(1,013,000)
Wells Fargo Bank Two
Derivative [Line Items]
Derivative, Maturity date	Oct. 31, 2024
Derivative, Fixed rate	2.72%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 15,000,000
Fair Value	$ (510,000)	$ (732,000)
Wells Fargo Bank Three
Derivative [Line Items]
Derivative, Maturity date	Jan. 31, 2028
Derivative, Fixed rate	2.37%
Variable Rate Index	LIBOR 1 month
Notional Amount	$ 75,000,000
Fair Value	$ (590,000)

X

- Definition

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

+ References

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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Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

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- Definition

Fixed interest rate related to the interest rate derivative.

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- Definition

Reference to the index or unit of measurement for the underlying which establishes the pricing terms of the derivative instrument. For example, the basis on the underlying for a natural gas futures contract might be the NYMEX price per million British thermal units (MMBtu).

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