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, 2016	Dec. 31, 2015	Dec. 31, 2014
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	$ 107,784	$ 113,733
Interest cost	4,972	4,816	$ 4,895
Plan amendments	0	827
Actuarial loss (gain)	1,794	(6,698)
Benefits paid	(3,235)	(4,894)
Projected benefit obligation at end of year	111,315	107,784	113,733
Change in plan assets:
Plan assets at fair value at beginning of year	86,292	90,320
Actual return on plan assets	3,642	866
Employer contribution	0	0
Benefits paid	(3,235)	(4,894)
Plan assets at fair value at end of year	86,699	86,292	$ 90,320
Funded status	$ (24,616)	$ (21,492)