Derivatives (Tables)

6 Months Ended

Jun. 30, 2015

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Schedule of Derivative Instruments

The following table provides a detail of the swaps outstanding and the related hedged items as of June 30, 2015:

	Maturity date	Face value of medium-term notes	Aggregate  notional amount of interest rate swaps	Fixed interest  rate	Weighted-average variable interest rate on hedged debt as of June 30,
Issuance date					2015	2014
		(Dollars in thousands)
May 2011	June 2017	$350,000	$150,000	3.50%	1.49%	1.42%
November 2013	November 2018	$300,000	$100,000	2.45%	1.23%	1.18%
February 2014	June 2019	$350,000	$100,000	2.55%	1.15%	1.10%
May 2014	September 2019	$400,000	$100,000	2.45%	0.90%	0.85%
February 2015	March 2020	$400,000	$150,000	2.65%	1.14%	—