Derivative Financial Instruments - Fair Value of Derivatives (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	May 26, 2014
Derivatives, Fair Value [Line Items]
Document Fiscal Year Focus	2014
Current Fiscal Year End Date	--12-31
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 432,483,000
Long-term Debt, Maturities, Repayments of Principal in Year Two	47,577,000
Long-term Debt, Maturities, Repayments of Principal in Year Three	521,606,000
Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	220,000,000
Derivative @ 2.087% 75K [Member]
Derivatives, Fair Value [Line Items]
Derivative, Inception Date	Apr. 15, 2014
Derivative, Maturity Date	Apr. 15, 2024
Derivative, Early Termination Date	Oct. 15, 2014
Derivative, Notional Amount	75,000,000
Derivative, Underlying Basis	3 Month LIBOR
Derivative, Fixed Interest Rate	2.087%
Derivative Asset, Fair Value, Gross Asset	0	7,476,000
Derivative Liability, Fair Value, Gross Liability	0	0
Derivative @ 2.088% 50K [Member]
Derivatives, Fair Value [Line Items]
Derivative, Inception Date	Apr. 15, 2014
Derivative, Maturity Date	Apr. 15, 2024
Derivative, Early Termination Date	Oct. 15, 2014
Derivative, Notional Amount	50,000,000
Derivative, Underlying Basis	3 Month LIBOR
Derivative, Fixed Interest Rate	2.088%
Derivative Asset, Fair Value, Gross Asset	0	4,978,000
Derivative Liability, Fair Value, Gross Liability	0	0
Derivative @ 2.873% 35K [Member]
Derivatives, Fair Value [Line Items]
Derivative, Inception Date	Apr. 15, 2014
Derivative, Maturity Date	Apr. 15, 2024
Derivative, Early Termination Date	Oct. 15, 2014
Derivative, Notional Amount	35,000,000
Derivative, Underlying Basis	3 Month LIBOR
Derivative, Fixed Interest Rate	2.8725%
Derivative Asset, Fair Value, Gross Asset	0	(1,036,000)
Derivative Liability, Fair Value, Gross Liability	0	0
Derivative @ 2.864% 60K [Member]
Derivatives, Fair Value [Line Items]
Derivative, Inception Date	Apr. 15, 2014
Derivative, Maturity Date	Apr. 15, 2024
Derivative, Early Termination Date	Oct. 15, 2014
Derivative, Notional Amount	60,000,000
Derivative, Underlying Basis	3 Month LIBOR
Derivative, Fixed Interest Rate	2.864%
Derivative Asset, Fair Value, Gross Asset	0	(1,821,000)
Derivative Liability, Fair Value, Gross Liability	0	0
Derivative @ 2.479% 75K [Member]
Derivatives, Fair Value [Line Items]
Derivative, Inception Date	Aug. 01, 2015
Derivative, Maturity Date	Aug. 01, 2025
Derivative, Early Termination Date	Feb. 01, 2016
Derivative, Notional Amount	75,000,000
Derivative, Underlying Basis	3 Month LIBOR
Derivative, Fixed Interest Rate	2.479%
Derivative Asset, Fair Value, Gross Asset	0	8,516,000
Derivative Liability, Fair Value, Gross Liability	(289,000)	0
Derivative A @ 2.479% 50K [Member]
Derivatives, Fair Value [Line Items]
Derivative, Inception Date	Aug. 01, 2015
Derivative, Maturity Date	Aug. 01, 2025
Derivative, Early Termination Date	Feb. 01, 2016
Derivative, Notional Amount	50,000,000
Derivative, Underlying Basis	3 Month LIBOR
Derivative, Fixed Interest Rate	2.479%
Derivative Asset, Fair Value, Gross Asset	0	5,670,000
Derivative Liability, Fair Value, Gross Liability	(193,000)	0
Derivative B @ 2.479% 50K [Member]
Derivatives, Fair Value [Line Items]
Derivative, Inception Date	Aug. 01, 2015
Derivative, Maturity Date	Aug. 01, 2025
Derivative, Early Termination Date	Feb. 01, 2016
Derivative, Notional Amount	50,000,000
Derivative, Underlying Basis	3 Month LIBOR
Derivative, Fixed Interest Rate	2.479%
Derivative Asset, Fair Value, Gross Asset	0	5,658,000
Derivative Liability, Fair Value, Gross Liability	(193,000)	0
Derivative @ 2.196% 28.1K [Member]
Derivatives, Fair Value [Line Items]
Derivative, Inception Date	Oct. 16, 2013
Derivative, Maturity Date	Oct. 16, 2020
Derivative, Notional Amount	28,100,000
Derivative, Underlying Basis	1 Month LIBOR
Derivative, Fixed Interest Rate	2.196%
Derivative Asset, Fair Value, Gross Asset	0	82,000
Derivative Liability, Fair Value, Gross Liability	(764,000)	0
Derivative @ 3.41% 45K [Member] [Member]
Derivatives, Fair Value [Line Items]
Derivative, Inception Date	Aug. 01, 2015
Derivative, Maturity Date	Aug. 01, 2025
Derivative, Early Termination Date	Feb. 01, 2016
Derivative, Notional Amount	45,000,000
Derivative, Underlying Basis	3 Month LIBOR
Derivative, Fixed Interest Rate	3.4115%
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	(3,964,000)	0
.76% Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative, Inception Date	Oct. 01, 2011
Derivative, Maturity Date	Sep. 01, 2014
Derivative, Notional Amount	9,000,000
Derivative, Underlying Basis	1 Month LIBOR
Derivative, Fixed Interest Rate	0.76%
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	0	34,000
Derivative @ 3.488% 20K [Member]
Derivatives, Fair Value [Line Items]
Derivative, Inception Date	Jun. 15, 2017
Derivative, Maturity Date	Jun. 15, 2027
Derivative, Early Termination Date	Dec. 15, 2017
Derivative, Notional Amount	20,000,000
Derivative, Underlying Basis	3 Month LIBOR
Derivative, Fixed Interest Rate	3.4875%
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	(1,227,000)	0
Derivative @ 3.48% 100K [Member]
Derivatives, Fair Value [Line Items]
Derivative, Inception Date	Jun. 15, 2017
Derivative, Maturity Date	Jun. 15, 2027
Derivative, Early Termination Date	Dec. 15, 2017
Derivative, Notional Amount	100,000,000
Derivative, Underlying Basis	3 Month LIBOR
Derivative, Fixed Interest Rate	3.48%
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	(6,080,000)	0
Derivative @ 3.48% 100K 2 [Member]
Derivatives, Fair Value [Line Items]
Derivative, Inception Date	Jun. 15, 2017
Derivative, Maturity Date	Jun. 15, 2027
Derivative, Early Termination Date	Dec. 15, 2017
Derivative, Notional Amount	100,000,000
Derivative, Underlying Basis	3 Month LIBOR
Derivative, Fixed Interest Rate	3.48%
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	(6,084,000)	0
Unsecured Maturities [Member]
Derivatives, Fair Value [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	350,000,000
Long-term Debt, Maturities, Repayments of Principal in Year Two	0
Long-term Debt, Maturities, Repayments of Principal in Year Three	400,000,000
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	35,237,000
Derivative Liability, Fair Value, Gross Liability	18,794,000	34,000
3.75% unsecured maturing 6/15/24 [Member] | Unsecured Debt [Member]
Derivatives, Fair Value [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.75%
Net cash proceeds from settlement of derivatives			4,600,000
Debt Instrument, Interest Rate, Effective Percentage			0.00%
Debt Instrument, Face Amount			$ 250,000,000