Qualified Employee Benefit Plans - The Retirement Plan's Projected Benefit Obligation, Fair Value of Plan Assets and Funded Status (Details) - Retirement Plan [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	$ 113,733	$ 93,548
Interest cost	4,816	4,895	$ 4,640
Plan amendments	827	0
Actuarial (gain) loss	(6,698)	19,909
Benefits paid	(4,894)	(4,619)
Projected benefit obligation at end of year	107,784	113,733	93,548
Change in plan assets:
Plan assets at fair value at beginning of year	90,320	83,831
Actual return on plan assets	866	5,108
Employer contribution	0	6,000
Benefits paid	(4,894)	(4,619)
Plan assets at fair value at end of year	86,292	90,320	$ 83,831
Funded status	$ (21,492)	$ (23,413)