Defined Benefit Pension Plans Amounts reported in accumulated other comprehensive income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Amounts reported in accumulated other comprehensive income
Unrecognized net actuarial loss, pretax	$ 10,675	$ 11,836
Unrecognized net actuarial loss, net of tax	6,456	7,150
Unrecognized prior service cost, pretax	341	0
Unrecognized prior service cost, net of tax	206	0
Amounts reported in accumulated other comprehensive income, pretax	11,016	11,836
Amounts reported in accumulated other comprehensive income, net of tax	6,662	7,150
Amortization of Costs Expected to be Recognized Next Year
Unrecognized net actuarial loss, pretax	949
Unrecognized net actuarial loss, net of tax	569
Unrecognized prior service cost, pretax	64
Unrecognized prior service cost, net of tax	38
Amortization of costs expected to be recognized next year, pretax	1,013
Amortization of costs expected to be recognized next year, net of tax	607
For pension plans with accumulated benefit obligations in excess of plan assets
Projected benefit obligation	24,833	27,228	$ 35,876
Accumulated benefit obligation	24,833	27,228
Fair value of plan assets	$ 11,509	$ 15,216	$ 21,567