Employee Benefit Plans - Profit Sharing and Savings Plans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits
Eligibility requirement, service hours to be completed	20 hours
Deferred Profit Sharing
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits
Eligibility requirement, requisite service period	3 years
Compensation expense	$ 1,600,000	$ 2,700,000	$ 700,000
Savings Plan, Employee Elected
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits
Compensation expense	5,500,000	$ 4,800,000	$ 4,700,000
Maximum annual contribution per employee, amount per dollar of employee contribution	$ 1.25
Maximum annual contribution per employee, percent	4.00%