Employee Benefit Plans - Narrative (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) hour	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Expense recognized related to qualified defined contribution benefit plan	$ 14,937,000	$ 12,364,000	$ 13,016,000
Select group of management and highly compensated individuals
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Participant balances, reflected in other liabilities	$ 27,284,000	$ 21,758,000
Defined Benefit Pension Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Number of hours of service | hour	1,000
Curtailments	$ (17,244,000)
Prior service cost recorded in OCI	1,852,000
Actuarial loss recognized from OCI to offset net curtailment gain	15,392,000
Net impact to income statement	0
Post-Retirement Medical Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Payments to medical and retirement plans	795,000
Supplemental Executive Retirement Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Payments to medical and retirement plans	$ 2,515,000