Employee Benefits - Components of Net Periodic Pension Cost and Other Changes in Plan Assets and Benefit Obligation Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components of Net Periodic Pension Cost
Service cost—benefits earned during the period	$ 463	$ 2,601	$ 2,369
Interest cost on projected benefit obligation	4,296	4,425	4,470
Expected return on plan assets	(5,780)	(7,180)	(6,907)
Amortization of prior service credit	(11)	(138)	(137)
Recognized net actuarial loss	2,345	2,028	941
Curtailment (gain)	(1,017)	0	0
Net Periodic Pension Expense	296	1,736	736
Other Changes in Plan Assets and Benefit Obligation Recognized in Other Comprehensive Income (Loss)
Net actuarial (gain) loss	(6,018)	5,678	13,294
Recognized net actuarial loss	(2,345)	(2,028)	(941)
Recognized prior service credit	1,029	138	137
Total (Before Tax Effects)	(7,334)	3,788	12,490
Total Recognized in Net Benefit Cost and Other Comprehensive (Loss)/Income (Before Tax Effects)	$ (7,038)	$ 5,524	$ 13,226