Employee Benefit Plans - Plan Assets and Projected Benefit Payments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension
Fair value of plan assets	$ 167,843	$ 156,678
Actuarial assumptions:
Expected rate of return on plan assets for 2016 net periodic benefit cost (as a percent)	7.00%
Equity securities
Pension
Target allocations for plan assets (as a percent)	65.00%
Common Stock
Pension
Fair value of plan assets	$ 10,201	8,954
Equity funds - large cap index
Pension
Fair value of plan assets	$ 93,576	85,874
Fixed income securities
Pension
Target allocations for plan assets (as a percent)	35.00%
Fixed income funds - diversified bond
Pension
Fair value of plan assets	$ 63,613	61,300
Short term investment funds
Pension
Fair value of plan assets	453	550
Quoted Prices in Active Markets for Identical Assets (Level 1)
Pension
Fair value of plan assets	10,201	8,954
Quoted Prices in Active Markets for Identical Assets (Level 1) | Common Stock
Pension
Fair value of plan assets	10,201	8,954
Significant other observable inputs (Level 2)
Pension
Fair value of plan assets	157,642	147,724
Significant other observable inputs (Level 2) | Equity funds - large cap index
Pension
Fair value of plan assets	93,576	85,874
Significant other observable inputs (Level 2) | Fixed income funds - diversified bond
Pension
Fair value of plan assets	63,613	61,300
Significant other observable inputs (Level 2) | Short term investment funds
Pension
Fair value of plan assets	453	550
Pension
Pension
Fair value of plan assets	167,843	$ 156,678	$ 206,309
Expected company contribution	4,800
Projected benefit payments
2017	36,396
2018	16,592
2019	13,013
2020	13,261
2021	12,470
2022 through 2026	59,733
Projected benefit payments	151,465
Other Postretirement Benefits
Pension
Expected company contribution	3,300
Projected benefit payments
2017	3,332
2018	3,637
2019	3,749
2020	3,872
2021	3,938
2022 through 2026	19,560
Projected benefit payments	38,088
Annual effects of one-percentage point change in the assumed health care cost trend rates
1-Percentage Point Increase, Effect on total of service and interest costs components	335
1-Percentage Point Decrease, Effect on total of service and interest costs components	(264)
1-Percentage Point Increase, Effect on postretirement benefit obligation	7,012
1-Percentage Point Decrease, Effect on postretirement benefit obligation	$ (5,524)