Derivatives (Details) (USD $)	3 Months Ended		6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Assets [Member]	Jun. 30, 2014 Derivative [Member]	Jun. 30, 2014 .76% Derivative [Member]		Dec. 31, 2013 .76% Derivative [Member]		Jun. 30, 2014 Derivative @ 2.196% 28.1K [Member]		Dec. 31, 2013 Derivative @ 2.196% 28.1K [Member]		Jun. 30, 2014 Derivative B @ 2.479% 50K [Member] [Member]		Dec. 31, 2013 Derivative B @ 2.479% 50K [Member] [Member]		Jun. 30, 2014 Derivative @ 2.873% 35K [Member]		Dec. 31, 2013 Derivative @ 2.873% 35K [Member]		Jun. 30, 2014 Derivative @ 2.864% 60K [Member]		Dec. 31, 2013 Derivative @ 2.864% 60K [Member]		Jun. 30, 2014 Derivative @ 2.087% 75K [Member]		Dec. 31, 2013 Derivative @ 2.087% 75K [Member]		Jun. 30, 2014 Derivative @ 2.088% 50K [Member]		Dec. 31, 2013 Derivative @ 2.088% 50K [Member]		Jun. 30, 2014 Derivative @ 2.479% 75K [Member]		Dec. 31, 2013 Derivative @ 2.479% 75K [Member]		Jun. 30, 2014 Derivative A @ 2.479% 50K [Member]		Dec. 31, 2013 Derivative A @ 2.479% 50K [Member]		Jun. 30, 2014 Derivative @ 3.41% 45K [Member] [Member]		Dec. 31, 2013 Derivative @ 3.41% 45K [Member] [Member]		Jun. 30, 2014 Swap [Member]	Jun. 30, 2014 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]		Dec. 31, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]		Dec. 31, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member] .76% Derivative [Member]		May 26, 2014 3.75% unsecured maturing 6/15/24 [Member] Unsecured Debt [Member]
Derivative [Line Items]
Document Period End Date			Jun. 30, 2014
Debt Instrument, Face Amount																																																						$ 250,000,000
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%
Document Fiscal Year Focus			2014
Derivative, Inception Date							Oct. 01, 2011				Oct. 16, 2013				Aug. 01, 2015				Apr. 15, 2014				Apr. 15, 2014				Apr. 15, 2014				Apr. 15, 2014				Aug. 01, 2015				Aug. 01, 2015				Aug. 01, 2015
Derivative, Maturity Date							Sep. 01, 2014				Oct. 16, 2020				Aug. 01, 2025				Apr. 15, 2024				Apr. 15, 2024				Apr. 15, 2024				Apr. 15, 2024				Aug. 01, 2025				Aug. 01, 2025				Aug. 01, 2025
Derivative, Early Termination Date															Feb. 01, 2016	[1]			Oct. 15, 2014	[1]			Oct. 15, 2014	[1]			Oct. 15, 2014	[1]			Oct. 15, 2014	[1]			Feb. 01, 2016	[1]			Feb. 01, 2016	[1]			Feb. 01, 2016	[1]
Derivative, Notional Amount					220,000,000		9,000,000				28,100,000				50,000,000				35,000,000				60,000,000				75,000,000				50,000,000				75,000,000				50,000,000				45,000,000
Derivative, Description of Variable Rate Basis							1 Month LIBOR				1 Month LIBOR				3 Month LIBOR				3 Month LIBOR				3 Month LIBOR				3 Month LIBOR				3 Month LIBOR				3 Month LIBOR				3 Month LIBOR				3 Month LIBOR
Derivative, Fixed Interest Rate							0.76%				2.196%				2.479%				2.8725%				2.864%				2.087%				2.088%				2.479%				2.479%				3.4115%
Derivative, Fixed Interest Rate						2.67%
Derivative Asset, Fair Value, Gross Asset							0	[2]	0	[2]	0	[2]	(82,000)	[2]	(2,320,000)	[2]	(5,658,000)	[2]	0	[2]	(1,036,000)	[2]	0	[2]	(1,821,000)	[2]	0	[2]	(7,476,000)	[2]	0	[2]	(4,978,000)	[2]	(3,484,000)	[2]	(8,516,000)	[2]	(2,322,000)	[2]	(5,670,000)	[2]	0	[2]	0	[2]		(8,126,000)	[2]	(35,237,000)	[2]
Derivative Liability, Fair Value, Gross Liability							(10,000)	[2]			(589,000)	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	(1,609,000)	[2]	0	[2]		2,208,000	[2]	34,000	[2]	34,000	[2]
Effective portion of change in fair value of derivative instruments	(11,153,000)	18,332,000	(24,953,000)	21,704,000
Amount reclassified from accumulated other comprehensive loss	(2,275,000)	(2,366,000)	(4,749,000)	(4,732,000)
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	0	0	0	(3,000)
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months			$ 9,000,000																																												$ 8,400,000

[1] Represents the date specified in the agreement for either optional or mandatory early termination which will result in cash settlement.

[2] The Company issued $250 million of new 3.75%, fixed rate ten year unsecured bonds in May 2014. Prior to issuing the bonds, the Company locked in the ten year treasury rate using forward starting interest rate swaps to mitigate the risk of interest rates rising. In connection with the issuance of the new bonds, the Company terminated and settled these swaps, resulting in net cash proceeds of $4.6 million. These proceeds will offset bond interest expense over the life of the bonds, resulting in a lower effective interest rate of 3.59%.