Employee Benefit Plans - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 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
Settlement charges	3,300,000	$ 2,500,000
Postretirement Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Curtailment gain	$ 816,000	0
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Settlement charges		$ 200,000