Retirement Plans (Tables)

3 Months Ended

Mar. 31, 2015

Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]

Net period benefit cost for the pension and postretirement plans

	Three Months Ended March 31,						Year Ended December 31,
	2015			2014			2014
	($ in Thousands)
Components of Net Periodic Benefit Cost
Pension Plan:
Service cost	$	3,063		$	2,975		$	11,058
Interest cost	1,642			1,790			7,132
Expected return on plan assets	(5,350		)	(4,855		)	(19,922		)
Amortization of prior service cost	13			15			58
Amortization of actuarial loss	532			325			1,384
Total net periodic benefit cost	$	(100	)	$	250		$	(290	)
Postretirement Plan:
Interest cost	$	35		$	39		$	150
Amortization of actuarial gain	—			(9		)	(35		)
Total net periodic benefit cost	$	35		$	30		$	115