Employee Benefit Plans (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Amounts recognized in consolidated balance sheets:
Accumulated other comprehensive income (loss)	$ (207,732)	$ (125,453)
Information regarding amounts in accumulated other comprehensive income (loss) that have not yet been recognized as components of net periodic benefit cost
Net gain (loss), gross	(163,809)
Net prior service (cost) credit, Gross	557
Amounts in accumulated other comprehensive income (loss) that have not yet been recognized as components of net periodic benefit cost, Gross	(163,252)
Net gain (loss), Net of tax	(106,475)
Net prior service (cost) credit, Net of tax	363
Amounts in accumulated other comprehensive income (loss) that have not yet been recognized as components of net periodic benefit cost, Net of tax	(106,112)
Amounts in accumulated other comprehensive income (loss) that are expected to be recognized as components of net periodic benefit costs during the next fiscal year
Net gain (loss), Gross	(12,080)
Net prior service (cost) credit, Gross	723
Amounts in accumulated other comprehensive income (loss) that are expected to be recognized as components of net periodic benefit costs during the next fiscal year, Gross	(11,357)
Net gain (loss), Net of tax	(7,852)
Net prior service (cost) credit, Net of tax	471
Amounts in accumulated other comprehensive income (loss) that are expected to be recognized as components of net periodic benefit costs during the next fiscal year, Net of tax	(7,381)
Other liabilities
Amounts recognized in consolidated balance sheets:
Accumulated other comprehensive income (loss)	(207,732)	(125,453)
Accumulated other comprehensive income (loss)
Amounts recognized in consolidated balance sheets:
Accumulated other comprehensive income (loss)	(163,252)	(67,366)
Defined Benefit Pension Plan
Amounts recognized in consolidated balance sheets:
Accumulated other comprehensive income (loss)	(139,118)	(52,067)
Information regarding amounts in accumulated other comprehensive income (loss) that have not yet been recognized as components of net periodic benefit cost
Net gain (loss), gross	(165,639)
Net prior service (cost) credit, Gross	(13)
Amounts in accumulated other comprehensive income (loss) that have not yet been recognized as components of net periodic benefit cost, Gross	(165,652)
Net gain (loss), Net of tax	(107,665)
Net prior service (cost) credit, Net of tax	(8)
Amounts in accumulated other comprehensive income (loss) that have not yet been recognized as components of net periodic benefit cost, Net of tax	(107,673)
Amounts in accumulated other comprehensive income (loss) that are expected to be recognized as components of net periodic benefit costs during the next fiscal year
Net gain (loss), Gross	(12,023)
Net prior service (cost) credit, Gross	(13)
Amounts in accumulated other comprehensive income (loss) that are expected to be recognized as components of net periodic benefit costs during the next fiscal year, Gross	(12,036)
Net gain (loss), Net of tax	(7,815)
Net prior service (cost) credit, Net of tax	(8)
Amounts in accumulated other comprehensive income (loss) that are expected to be recognized as components of net periodic benefit costs during the next fiscal year, Net of tax	(7,823)
Defined Benefit Pension Plan | Other liabilities
Amounts recognized in consolidated balance sheets:
Accumulated other comprehensive income (loss)	(139,118)	(52,067)
Defined Benefit Pension Plan | Accumulated other comprehensive income (loss)
Amounts recognized in consolidated balance sheets:
Accumulated other comprehensive income (loss)	(165,652)	(69,564)
Post-Retirement Medical Plan
Amounts recognized in consolidated balance sheets:
Accumulated other comprehensive income (loss)	(12,782)	(11,081)
Information regarding amounts in accumulated other comprehensive income (loss) that have not yet been recognized as components of net periodic benefit cost
Net gain (loss), gross	10,686
Net prior service (cost) credit, Gross	3,704
Amounts in accumulated other comprehensive income (loss) that have not yet been recognized as components of net periodic benefit cost, Gross	14,390
Net gain (loss), Net of tax	6,946
Net prior service (cost) credit, Net of tax	2,408
Amounts in accumulated other comprehensive income (loss) that have not yet been recognized as components of net periodic benefit cost, Net of tax	9,354
Amounts in accumulated other comprehensive income (loss) that are expected to be recognized as components of net periodic benefit costs during the next fiscal year
Net gain (loss), Gross	606
Net prior service (cost) credit, Gross	1,669
Amounts in accumulated other comprehensive income (loss) that are expected to be recognized as components of net periodic benefit costs during the next fiscal year, Gross	2,275
Net gain (loss), Net of tax	394
Net prior service (cost) credit, Net of tax	1,085
Amounts in accumulated other comprehensive income (loss) that are expected to be recognized as components of net periodic benefit costs during the next fiscal year, Net of tax	1,479
Post-Retirement Medical Plan | Other liabilities
Amounts recognized in consolidated balance sheets:
Accumulated other comprehensive income (loss)	(12,782)	(11,081)
Post-Retirement Medical Plan | Accumulated other comprehensive income (loss)
Amounts recognized in consolidated balance sheets:
Accumulated other comprehensive income (loss)	14,390	13,885
Supplemental Executive Retirement Plan
Amounts recognized in consolidated balance sheets:
Accumulated other comprehensive income (loss)	(55,832)	(62,305)
Information regarding amounts in accumulated other comprehensive income (loss) that have not yet been recognized as components of net periodic benefit cost
Net gain (loss), gross	(8,856)
Net prior service (cost) credit, Gross	(3,134)
Amounts in accumulated other comprehensive income (loss) that have not yet been recognized as components of net periodic benefit cost, Gross	(11,990)
Net gain (loss), Net of tax	(5,756)
Net prior service (cost) credit, Net of tax	(2,037)
Amounts in accumulated other comprehensive income (loss) that have not yet been recognized as components of net periodic benefit cost, Net of tax	(7,793)
Amounts in accumulated other comprehensive income (loss) that are expected to be recognized as components of net periodic benefit costs during the next fiscal year
Net gain (loss), Gross	(663)
Net prior service (cost) credit, Gross	(933)
Amounts in accumulated other comprehensive income (loss) that are expected to be recognized as components of net periodic benefit costs during the next fiscal year, Gross	(1,596)
Net gain (loss), Net of tax	(431)
Net prior service (cost) credit, Net of tax	(606)
Amounts in accumulated other comprehensive income (loss) that are expected to be recognized as components of net periodic benefit costs during the next fiscal year, Net of tax	(1,037)
Supplemental Executive Retirement Plan | Other liabilities
Amounts recognized in consolidated balance sheets:
Accumulated other comprehensive income (loss)	(55,832)	(62,305)
Supplemental Executive Retirement Plan | Accumulated other comprehensive income (loss)
Amounts recognized in consolidated balance sheets:
Accumulated other comprehensive income (loss)	$ (11,990)	$ (11,687)