Pension and Severance Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Compensation and Retirement Disclosure [Abstract]
Service cost	$ 1,958	$ 1,855	$ 5,873	$ 5,565
Interest on projected benefit obligation	1,320	1,411	3,961	4,241
Expected return on plan assets	(248)	(334)	(745)	(1,005)
Recognized actuarial loss	250	265	785	797
Amortization of prior service cost	32	32	96	96
Defined benefit and severance plan expense	$ 3,312	$ 3,229	$ 9,970	$ 9,694