Significant Accounting Policies - Components of Net Periodic Pension Cost of Defined Benefit Plan Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accounting Policies [Abstract]
Service cost	$ 35	$ 16	$ 51	$ 31
Interest cost	11	9	21	19
Amortization of prior service cost	21	21	42	41
Net periodic benefit cost	$ 67	$ 46	$ 114	$ 91