Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Interest Spread on Interest Rate Swaps (Details)

v3.8.0.1
Derivative Instruments and Hedging Activities Interest Spread on Interest Rate Swaps (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]        
Average Notional Amount $ 18,317,731,000 $ 20,642,679,000 $ 17,799,927,000 $ 22,701,140,000
Interest Rate Swap [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Interest Expense on Interest Rate Swap and Swaption Agreements $ 389,000 $ 4,294,000 $ 10,867,000 $ 18,140,000