Derivative Instruments (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2015	Dec. 31, 2014
Not Designated as Hedging Instrument [Member]
Interest rate swap agreements [Abstract]
Notional amount of interest rate swap		$ 687,484	$ 502,642
Estimated fair value of interest rate swap		$ (609)	$ (405)
Designated as Hedging Instrument [Member]
Forward Cash Flow Hedge Relationship [Abstract]
Lower maturity range date term		Jul. 01, 2014	Jul. 01, 2014
Higher maturity range date term		Jul. 01, 2021	Jul. 01, 2021
Pay Fixed / Receive Variable Swaps [Member] | Not Designated as Hedging Instrument [Member]
Interest rate swap agreements [Abstract]
Notional amount of interest rate swap		$ 343,742	$ 251,321
Estimated fair value of interest rate swap		18,572	13,030
Pay Variable / Receive Fixed Swaps [Member] | Not Designated as Hedging Instrument [Member]
Interest rate swap agreements [Abstract]
Notional amount of interest rate swap		343,742	251,321
Estimated fair value of interest rate swap		$ (19,181)	$ (13,435)
Interest Rate Swap April 2016 April 2020 [Member] | Designated as Hedging Instrument [Member]
Forward Cash Flow Hedge Relationship [Abstract]
Lower maturity range date term	[1]	Apr. 01, 2016	Apr. 01, 2016
Forecasted notional amount		$ 33,000	$ 33,000
Variable interest rate		3 month LIBOR	3 month LIBOR
Fixed interest rate		2.265%	2.265%
Higher maturity range date term	[1]	Apr. 01, 2020	Apr. 01, 2020
Interest rate derivative assets, at fair value		$ (1,131)	$ (96)
Unrealized gain in accumulated other comprehensive income		$ (687)	$ (58)
Interest Rate Swap April 2016 April 2022 [Member] | Designated as Hedging Instrument [Member]
Forward Cash Flow Hedge Relationship [Abstract]
Lower maturity range date term	[1]	Apr. 01, 2016	Apr. 01, 2016
Forecasted notional amount		$ 33,000	$ 33,000
Variable interest rate		3 month LIBOR	3 month LIBOR
Fixed interest rate		2.646%	2.646%
Higher maturity range date term	[1]	Apr. 01, 2022	Apr. 01, 2022
Interest rate derivative assets, at fair value		$ (1,840)	$ (531)
Unrealized gain in accumulated other comprehensive income		$ (1,118)	$ (323)
Interest Rate Swap October 2016 October 2020 [Member] | Designated as Hedging Instrument [Member]
Forward Cash Flow Hedge Relationship [Abstract]
Lower maturity range date term	[1]	Oct. 01, 2016	Oct. 01, 2016
Forecasted notional amount		$ 33,000	$ 33,000
Variable interest rate		3 month LIBOR	3 month LIBOR
Fixed interest rate		2.523%	2.523%
Higher maturity range date term	[1]	Oct. 01, 2020	Oct. 01, 2020
Interest rate derivative assets, at fair value		$ (1,235)	$ (210)
Unrealized gain in accumulated other comprehensive income		(751)	(128)
Interest Rate Swap July 2014 July 2021 [Member] | Designated as Hedging Instrument [Member]
Forward Cash Flow Hedge Relationship [Abstract]
Forecasted notional amount		$ 27,500	$ 27,500
Variable interest rate		1 month LIBOR	1 month LIBOR
Fixed interest rate		2.09%	2.09%
Interest rate derivative assets, at fair value		$ 1,012	$ 941
Unrealized gain in accumulated other comprehensive income		$ 615	$ 572
Interest Rate Swap July 2014 July 2022 [Member] | Designated as Hedging Instrument [Member]
Forward Cash Flow Hedge Relationship [Abstract]
Lower maturity range date term		Jul. 01, 2014	Jul. 01, 2014
Forecasted notional amount		$ 25,000	$ 27,500
Variable interest rate		1 month LIBOR	1 month LIBOR
Fixed interest rate		2.27%	2.27%
Higher maturity range date term		Jul. 01, 2022	Jul. 01, 2022
Interest rate derivative assets, at fair value		$ 1,350	$ 409
Unrealized gain in accumulated other comprehensive income		$ 820	249
Interest Rate Swap July 2014 July 2023 [Member] | Designated as Hedging Instrument [Member]
Forward Cash Flow Hedge Relationship [Abstract]
Lower maturity range date term		Jul. 01, 2014
Forecasted notional amount		$ 27,500	$ 27,500
Variable interest rate		1 month LIBOR	1 month LIBOR
Fixed interest rate		2.42%	2.42%
Higher maturity range date term		Jul. 01, 2023	Jul. 01, 2023
Interest rate derivative assets, at fair value		$ 1,732	$ 651
Unrealized gain in accumulated other comprehensive income		1,053	396
Interest Rate Swap July 2014 July 2024 [Member] | Designated as Hedging Instrument [Member]
Forward Cash Flow Hedge Relationship [Abstract]
Forecasted notional amount		$ 30,000	$ 27,500
Variable interest rate		1 month LIBOR	1 month LIBOR
Fixed interest rate		2.50%	2.50%
Higher maturity range date term		Jul. 01, 2024	Jul. 01, 2024
Interest rate derivative assets, at fair value		$ 1,701	$ 956
Unrealized gain in accumulated other comprehensive income		$ 1,034	$ 581
Interest Rate Swap October 2017 October 2021 [Member] | Designated as Hedging Instrument [Member]
Forward Cash Flow Hedge Relationship [Abstract]
Lower maturity range date term	[1]	Oct. 01, 2017	Oct. 01, 2017
Forecasted notional amount		$ 33,000	$ 33,000
Variable interest rate		3 month LIBOR	3 month LIBOR
Fixed interest rate		2.992%	2.992%
Higher maturity range date term	[1]	Oct. 01, 2021	Oct. 01, 2021
Interest rate derivative assets, at fair value		$ (1,326)	$ (517)
Unrealized gain in accumulated other comprehensive income		$ (806)	$ (314)
Interest Rate Swap April 2018 July 2022 [Member] | Designated as Hedging Instrument [Member]
Forward Cash Flow Hedge Relationship [Abstract]
Lower maturity range date term	[1]	Apr. 01, 2018	Apr. 01, 2018
Forecasted notional amount		$ 34,000	$ 34,000
Variable interest rate		3 month LIBOR	3 month LIBOR
Fixed interest rate		3.118%	3.118%
Higher maturity range date term	[1]	Jul. 01, 2022	Jul. 01, 2022
Interest rate derivative assets, at fair value		$ (1,320)	$ (590)
Unrealized gain in accumulated other comprehensive income		$ (802)	$ (359)
Interest Rate Swap July 2018 October 2022 [Member] | Designated as Hedging Instrument [Member]
Forward Cash Flow Hedge Relationship [Abstract]
Lower maturity range date term	[1]	Jul. 01, 2018	Jul. 01, 2018
Forecasted notional amount		$ 34,000	$ 34,000
Variable interest rate		3 month LIBOR	3 month LIBOR
Fixed interest rate		3.158%	3.158%
Higher maturity range date term	[1]	Oct. 01, 2022	Oct. 01, 2022
Interest rate derivative assets, at fair value		$ (1,281)	$ (602)
Unrealized gain in accumulated other comprehensive income		$ (778)	$ (366)
Interest Rate Swap August 2015 - August 2018 [Member] | Designated as Hedging Instrument [Member]
Forward Cash Flow Hedge Relationship [Abstract]
Lower maturity range date term		Aug. 01, 2015
Forecasted notional amount		$ 15,000
Variable interest rate		1 month LIBOR
Fixed interest rate		1.048%
Higher maturity range date term		Aug. 01, 2018
Interest rate derivative assets, at fair value		$ 88
Unrealized gain in accumulated other comprehensive income		$ 53
Interest Rate Swap August 2015 - August 2019 [Member] | Designated as Hedging Instrument [Member]
Forward Cash Flow Hedge Relationship [Abstract]
Lower maturity range date term		Aug. 01, 2015
Forecasted notional amount		$ 15,000
Variable interest rate		1 month LIBOR
Fixed interest rate		1.281%
Higher maturity range date term		Aug. 01, 2019
Interest rate derivative assets, at fair value		$ 135
Unrealized gain in accumulated other comprehensive income		$ 82
Interest Rate Swap August 2015 - August 2020 [Member] | Designated as Hedging Instrument [Member]
Forward Cash Flow Hedge Relationship [Abstract]
Lower maturity range date term		Aug. 01, 2015
Forecasted notional amount		$ 15,000
Variable interest rate		1 month LIBOR
Fixed interest rate		1.47%
Higher maturity range date term		Aug. 01, 2020
Interest rate derivative assets, at fair value		$ 173
Unrealized gain in accumulated other comprehensive income		$ 105

[1] No cash will be exchanged prior to the term.