Pension Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Components of Net Periodic Benefit Costs for Both Pension Plans
Service cost	$ 1,987	$ 1,584
Interest cost	624	548
Expected return on plan assets that reduces periodic pension costs	(545)	(494)
Amortization of prior service costs	4	4
Amortization of net actuarial loss	372	172
Net periodic benefit cost	$ 2,442	$ 1,814