Derivatives (Additional Information) (Details) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Offsetting counterparty derivative instruments	$ 21,200,000	$ 23,100,000
Interest Rate Swap
Derivatives, Fair Value [Line Items]
Notional amount	$ 21,192,000.000	$ 23,104,000.000

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant