Fair Value Measurements Narrative (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Jun. 27, 2012	Aug. 25, 2010
Fair Value, Inputs, Level 1 [Member]
Fair Value Measurements [Line Items]
Defined benefit plan, transfers between measurement levels	$ 0	$ 0
Fair Value, Inputs, Level 2 [Member]
Fair Value Measurements [Line Items]
Defined benefit plan, transfers between measurement levels	0	0
Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements [Line Items]
Defined benefit plan, transfers between measurement levels	0	0
Senior Notes [Member] | $400 Million Senior Notes [Member]
Fair Value Measurements [Line Items]
Debt instrument face amount				$ 400,000,000
Senior Notes [Member] | $400 Million Senior Notes [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Measurements [Line Items]
Debt instrument fair value	435,000,000	435,000,000	$ 437,700,000
Senior Notes [Member] | $250 Million Senior Notes [Member]
Fair Value Measurements [Line Items]
Debt instrument face amount					$ 250,000,000
Senior Notes [Member] | $250 Million Senior Notes [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Measurements [Line Items]
Debt instrument fair value	$ 271,300,000	$ 271,300,000	$ 268,900,000