Derivative Instruments and Hedging Activities (Details) - Narrative - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative notional amount, cash flow hedge, received fixed pay variable interest rate swap	$ 710,000		$ 710,000
Derivative notional amount, cash flow hedge, forward starting interest rate swap	710,000		710,000
Derivative notional amount of cash flow hedge received, variable pay fixed interest rate swap	325,000		325,000
Interest rate cash flow hedge gain (loss) to be reclassified during the next 12 months, net	3,800		3,800
Derivative transaction fees	$ 2,100	$ 818	$ 5,300	$ 1,500
Portion of fair value of outstanding interest rate swaps covered by collateral agreements (percent)	100.00%		100.00%		100.00%