Derivatives (Details)		3 Months Ended
		Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Oct. 31, 2015 USD ($) instrument	May. 31, 2014 USD ($) instrument	Apr. 30, 2013 USD ($) instrument	Jun. 30, 2011 USD ($) instrument	Sep. 30, 2007 USD ($) instrument
Derivative [Line Items]
Fair value of interest rate hedges recognized in other comprehensive income		$ 24,351,000
Interest expense		695,000	$ 414,000
Interest rate hedges gain (loss) to be reclassified into interest expense over next 12 months		$ 2,894,000
Interest Rate Swap
Derivative [Line Items]
Number of derivatives | instrument								2
Aggregate Notional Amount								$ 100,000,000
Fair Value When Terminated								3,260,000
Fair Value Deferred In Other Comprehensive Income	[1]							$ 3,228,000
Treasury Lock
Derivative [Line Items]
Number of derivatives | instrument							2
Aggregate Notional Amount							$ 150,000,000
Fair Value When Terminated							5,300,000
Fair Value Deferred In Other Comprehensive Income	[1]						$ 5,218,000
Forward Swap
Derivative [Line Items]
Number of derivatives | instrument				4	3	4
Aggregate Notional Amount				$ 300,000,000	$ 225,000,000	$ 240,000,000
Fair Value When Terminated				13,369,000	6,312,000	3,156,000
Fair Value Deferred In Other Comprehensive Income	[1]			$ 13,369,000	$ 6,312,000	$ 3,141,000

[1] The amount reported in accumulated other comprehensive income will be reclassified to interest expense as interest payments are made on the related notes payable.