Employee Benefit Plans - Narrative (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) Retiree shares	Dec. 31, 2014 USD ($) Retiree shares	Dec. 31, 2013 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Liabilities, including the Company's common stock	$ 22,371,000	$ 28,932,000
Defined contribution cost recognized	$ (6,400,000)	$ (4,900,000)	$ 7,400,000
Postretirement Benefits Other than Pensions
Defined Benefit Plan Disclosure [Line Items]
Number of retirees and dependents | Retiree	276	278
Subsidy limit percentage of expected annual fully insured premium over age threshold	60.00%
Subsidy limit percentage of expected annual fully insured premium under age threshold	$ 648,000
Annual subsidy limit percentage increases for fully insured premium over age threshold	3.50%
Estimated contributions in 2016	$ 1,400,000
Savings Investment Plan
Defined Benefit Plan Disclosure [Line Items]
Employer matching percent	6.00%
Maximum contribution, percent of employee salary	9.00%
Plan contributions charged to expense	$ 7,100,000	$ 7,200,000	6,900,000
Deferred compensation plan
Defined Benefit Plan Disclosure [Line Items]
Market value of the trust assets, excluding the Company's common stock	12,900,000	13,100,000
Liabilities, including the Company's common stock	$ 22,400,000	$ 28,900,000
Number of common stock deferred into the rabbi trust (in shares) | shares	534,174	534,174
Company's common stock held in the rabbi trust	$ 5,700,000	$ 5,700,000
Plan contributions charged to expense	(6,400,000)
Company contributions to deferred compensation plan	$ 1,000,000	$ 800,000	$ 700,000