Derivative Instruments and Hedging Activities (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 swap	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative notional amount, cash flow hedge, forward starting interest rate swap	$ 325,000,000
Derivative, number of instruments held	4
Interest rate cash flow hedge gain (loss) to be reclassified during the next 12 months, net	5,000,000
Derivative Transaction Fees	$ 2,200,000	$ 2,800,000	$ 0
Portion of fair value outstanding, interest rate swaps covered by collateral agreements (percent)	100.00%	100.00%