Employee Benefit Plans - Additional Information (Details) - USD ($)	3 Months Ended				9 Months Ended
	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Non-Qualified Supplemental Employee Retirement Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions by employer		$ 14,500,000
Estimated amount of additional benefit payments					$ 0
Defined Benefit Plan, Settlements		3,300,000		$ 2,500,000
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Settlements			$ 500,000			$ 1,400,000
Postretirement Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Curtailment gain	$ 0	$ 800,000	$ 0		$ 816,000	$ 0