Derivative Instruments and Hedging Activities (Details) - Cash Flow Hedges - Cash Flow Hedging - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gross notional amount outstanding	$ 1,220,000	$ 650,000
Derivative asset fair value	12,784	1,166
Derivative liability fair value	$ (13,844)	$ (3,096)
Weighted-average interest rate received	1.23%	1.63%
Weighted-average interest rate paid	0.72%	0.16%
Weighted-average maturity (in years)	4 years 1 month 28 days	4 years 6 months 8 days