Qualified Employee Benefit Plans - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) investment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Contributions to qualified profit sharing plan	$ 14,400,000	$ 14,300,000	$ 14,200,000
Defined contribution expense for foreign entities	6,800,000	6,800,000	7,900,000
Other comprehensive (loss) gain	$ (3,193,000)
Return Seeking Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations, percent	40.00%
Risk Mitigating Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations, percent	15.00%
Diversifying Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations, percent	17.00%
Dynamic Asset Allocation [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations, percent	28.00%
Fixed Income Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Retirement plan, number of investments | investment	2
Equity Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Retirement plan, number of investments | investment	3
Private Investment Trusts Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Retirement plan, number of investments | investment	2
Minimum [Member] | Return Seeking Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations, percent	30.00%
Minimum [Member] | Risk Mitigating Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations, percent	10.00%
Minimum [Member] | Diversifying Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations, percent	0.00%
Minimum [Member] | Dynamic Asset Allocation [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations, percent	18.00%
Maximum [Member] | Return Seeking Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations, percent	60.00%
Maximum [Member] | Risk Mitigating Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations, percent	30.00%
Maximum [Member] | Diversifying Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations, percent	25.00%
Maximum [Member] | Dynamic Asset Allocation [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations, percent	38.00%
Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contribution	$ 4,000,000	0
Estimated employer contributions in 2018	5,000,000
Other comprehensive (loss) gain	(3,068,000)	(3,032,000)	1,888,000
Discount rate and lump sum interest rates	11,900,000	3,500,000	5,600,000
Changes in census data	1,400,000
Earnings of plan assets exceeding expectations	8,500,000	1,800,000	5,300,000
Actuarial loss	1,100,000
Mortality assumption	$ (700,000)	1,700,000	$ 1,400,000
Defined benefit plan, amortization period	32 years
Future amortization of prior service cost	$ 23,959
Loss to be amortized over next fiscal year	1,100,000
Accumulated benefit obligation	$ 125,200,000	$ 111,300,000
Assumptions used calculating benefit obligation, discount rate, percent	3.90%	4.55%
Expected long-term rate of return on plan assets	6.00%	6.50%	7.00%