Employee Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits
Change in benefit obligation
Benefit obligation at beginning of year	$ 8,677	$ 133,984
Service cost	0	236	$ 180
Interest cost	194	182	4,774
Actuarial (gains) losses	(421)	(6,299)
Participant contributions	0	0
Retiree drug subsidy received	0	0
Benefits paid	(1,338)	(119,426)
Benefit obligation at end of year	7,112	8,677	133,984
Change in plan assets
Fair value of plan assets at beginning of year	285	116,041
Actual gains on plan assets	0	517
Company contributions	1,053	3,153
Participant contributions	0	0
Benefits paid	(1,338)	(119,426)
Fair value of plan assets at end of year	0	285	116,041
Under funded status of plans at end of year	(7,112)	(8,392)
Postretirement Benefits
Change in benefit obligation
Benefit obligation at beginning of year	39,152	42,300
Service cost	760	900	687
Interest cost	1,549	1,584	1,511
Actuarial (gains) losses	(10,823)	(4,762)
Participant contributions	653	535
Retiree drug subsidy received	5	138
Benefits paid	(1,539)	(1,543)
Benefit obligation at end of year	29,757	39,152	42,300
Change in plan assets
Fair value of plan assets at beginning of year	0	0
Actual gains on plan assets	0	0
Company contributions	886	1,008
Participant contributions	653	535
Benefits paid	(1,539)	(1,543)
Fair value of plan assets at end of year	0	0	$ 0
Under funded status of plans at end of year	$ (29,757)	$ (39,152)