Employee Benefits - Components of Net Periodic Pension Cost and Other Changes in Plan Assets and Benefit (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Components of Net Periodic Pension Cost
Service cost—benefits earned during the period	$ 0	$ 0	$ 0	$ 474
Interest cost on projected benefit obligation	1,025	1,036	2,050	2,101
Expected return on plan assets	(1,582)	(1,434)	(3,164)	(2,893)
Amortization of prior service credit	475	(35)	949	(70)
Recognized net actuarial loss	0	526	0	1,070
Net Periodic Pension Expense	$ (82)	$ 93	$ (165)	$ 682