Pension and Severance Benefits - Unrecognized Costs (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
Unrecognized actuarial losses	$ 26,682	$ 18,438
Unrecognized prior service costs	$ 564	$ 692

Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost.

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