Employee Benefit Plans Employee Benefit Plans 2 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits
Change in Projected Benefit Obligation:
Projected benefit obligation at beginning of year	$ 168,934	$ 185,184
Service cost	5,094	6,276	$ 5,643
Interest cost	7,910	7,686	7,520
Actuarial (gain) loss	(4,162)	24,413
Benefits/expenses paid	(5,736)	(5,799)
Projected benefit obligation at end of year	180,364	168,934	185,184
Changes in Plan Assets:
Fair value of plan assets at beginning of year	142,174	140,561
Actual return on plan assets	9,182	673
Employer contributions	5,252	6,739
Benefits/expenses paid	(5,736)	(5,799)
Fair value of plan assets at end of year	150,872	142,174	140,561
Funded Status:
Net amount recognized as accrued pension cost	(29,492)	(26,760)
Post-Retirement Medical Benefits
Change in Projected Benefit Obligation:
Projected benefit obligation at beginning of year	9,393	12,326
Service cost	247	340	348
Interest cost	371	435	495
Actuarial (gain) loss	715	3,375
Benefits/expenses paid	(494)	(333)
Projected benefit obligation at end of year	8,802	9,393	12,326
Changes in Plan Assets:
Fair value of plan assets at beginning of year	10,614	10,723
Actual return on plan assets	418	115
Employer contributions	0	109
Benefits/expenses paid	(494)	(333)
Fair value of plan assets at end of year	10,538	10,614	$ 10,723
Funded Status:
Net amount recognized as accrued pension cost	$ 1,736	$ 1,221