Derivatives (Interest rate swap agreements) (Details) - Jun. 30, 2015 - USD ($) $ in Millions		Total
Swap Agreement Three [Member]
Swaps:
Original variable, rate debt amount		$ 300.0
Agreement date		Aug. 16, 2006
Effective date		Aug. 18, 2006
Expiration date		Aug. 10, 2018
Designed cash flow hedge date		Aug. 04, 2006
Swap Agreement Eight [Member]
Swaps:
Original variable, rate debt amount		$ 19.0
Agreement date		Aug. 27, 2008
Effective date		Aug. 29, 2008
Expiration date		Jul. 10, 2015
Designed cash flow hedge date		Apr. 10, 2008
Swap Agreement Nine [Member]
Swaps:
Original variable, rate debt amount		$ 30.0
Agreement date		Sep. 24, 2008
Effective date		Sep. 30, 2008
Expiration date		Sep. 10, 2015
Designed cash flow hedge date		Sep. 24, 2008
Swap Agreement Ten [Member]
Swaps:
Original variable, rate debt amount	[1]	$ 15.0
Agreement date		Mar. 24, 2009
Effective date		Mar. 30, 2009
Expiration date		Mar. 30, 2016
Designed cash flow hedge date		Mar. 25, 2009
Swap Agreement Eleven [Member]
Swaps:
Original variable, rate debt amount	[1]	$ 14.7
Agreement date		Jul. 06, 2010
Effective date		Aug. 15, 2010
Expiration date		Jul. 15, 2017
Designed cash flow hedge date		Jul. 06, 2010
Swap Agreement Twelve [Member]
Swaps:
Original variable, rate debt amount	[1]	$ 25.0
Agreement date		Apr. 26, 2011
Effective date		Jun. 01, 2011
Expiration date		Jun. 01, 2018
Designed cash flow hedge date		Jun. 01, 2011
Swap Agreement Thirteen [Member]
Swaps:
Original variable, rate debt amount	[1]	$ 50.0
Agreement date		Jul. 29, 2011
Effective date		Aug. 15, 2011
Expiration date		Aug. 15, 2018
Designed cash flow hedge date		Jul. 29, 2011
Swap Agreement Fourteen [Member]
Swaps:
Original variable, rate debt amount	[1]	$ 20.0
Agreement date		Aug. 03, 2011
Effective date		Sep. 12, 2011
Expiration date		Sep. 10, 2018
Designed cash flow hedge date		Aug. 03, 2011
Swap Agreement Fifteen [Member]
Swaps:
Original variable, rate debt amount	[2]	$ 15.1
Agreement date		Mar. 27, 2012
Effective date		Mar. 28, 2012
Expiration date		Mar. 28, 2019
Designed cash flow hedge date		Mar. 26, 2012
Swap Agreement Sixteen [Member]
Swaps:
Original variable, rate debt amount		$ 25.0
Agreement date		Apr. 13, 2012
Effective date		Apr. 16, 2012
Expiration date		Apr. 01, 2019
Designed cash flow hedge date		Apr. 12, 2012
Swap Agreement Seventeen [Member]
Swaps:
Original variable, rate debt amount		$ 44.3
Agreement date		Jan. 11, 2013
Effective date		Jan. 15, 2013
Expiration date		Dec. 15, 2019
Designed cash flow hedge date		Jan. 11, 2013

[1] forward swap

[2] operating lease