Employee Benefit Plans Employee Benefits Plans - Net Periodic Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Components of net periodic cost (benefit):
Service cost	$ 2,544	$ 3,839	$ 2,516	$ 7,241
Interest cost	6,711	7,012	20,139	20,814
Expected return on plan assets	(4,980)	(6,237)	(15,216)	(18,793)
Amortization of unrecognized prior service costs (benefits)	(109)	(150)	37	(452)
Amortization of losses (gains) from earlier periods	2,302	2,644	6,448	7,414
Net periodic cost (benefit)	6,468	7,108	13,924	16,224
Defined Benefit Pension Plan
Components of net periodic cost (benefit):
Service cost	2,170	3,417	1,436	6,087
Interest cost	6,114	6,384	18,356	18,948
Expected return on plan assets	(4,980)	(6,237)	(15,216)	(18,793)
Amortization of unrecognized prior service costs (benefits)	0	0	0	0
Amortization of losses (gains) from earlier periods	2,241	2,726	6,639	7,695
Net periodic cost (benefit)	5,545	6,290	11,215	13,937
Post-Retirement Medical Plan
Components of net periodic cost (benefit):
Service cost	378	349	1,092	935
Interest cost	192	184	568	534
Expected return on plan assets	0	0	0	0
Amortization of unrecognized prior service costs (benefits)	(235)	(275)	(339)	(827)
Amortization of losses (gains) from earlier periods	75	(67)	(151)	(237)
Net periodic cost (benefit)	410	191	1,170	405
Expected Employer obligation for the year	155	212	531	603
Supplemental Executive Retirement Plan
Components of net periodic cost (benefit):
Service cost	(4)	73	(12)	219
Interest cost	405	444	1,215	1,332
Expected return on plan assets	0	0	0	0
Amortization of unrecognized prior service costs (benefits)	126	125	376	375
Amortization of losses (gains) from earlier periods	(14)	(15)	(40)	(44)
Net periodic cost (benefit)	513	627	1,539	1,882
Expected Employer obligation for the year	$ 834	$ 834	$ 2,502	$ 2,502