Level 4 Retirement and Benefit Plans (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2013	Jun. 30, 2013	Jun. 30, 2012
Net periodic benefit cost [Abstract]
Service cost	$ 671,000	$ 1,182,000		$ 1,342,000	$ 2,351,000
Interest cost	4,650,000	4,824,000		9,292,000	9,667,000
Expected return on plan assets	(4,916,000)	(4,847,000)		(9,782,000)	(9,691,000)
Amortization of actuarial loss	2,281,000	1,958,000		4,537,000	3,984,000
Amortization of prior service costs	22,000	42,000		45,000	83,000
Net periodic benefit cost	2,708,000	3,159,000		5,434,000	6,394,000
Pension contributions [Abstract]
Pension contributions				9,970,000	7,874,000
Estimated remaining 2013 contributions			$ 1,000,000