Employee Benefits - Components of Net Periodic Pension Cost and Other Changes in Plan Assets and Benefit (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Components of Net Periodic Pension Cost
Service cost—benefits earned during the period	$ 0	$ 474
Interest cost on projected benefit obligation	1,025	1,065
Expected return on plan assets	(1,582)	(1,459)
Amortization of prior service credit	474	(35)
Recognized net actuarial loss	0	544
Net Periodic Pension Expense	$ (83)	$ 589