For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Accumulated Benefit Obligation
-URI http://asc.fasb.org/extlink&oid=6503844

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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Amount of benefits from a defined benefit plan expected to be paid in the five fiscal years after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

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Amount of discretionary contributions made by an employer to a defined contribution plan.

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Employee Benefit Plans - Qualified Pension Plan (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended
	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Voluntary contribution	$ 1,000
Pension plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair value of qualified plan assets		$ 42,061	$ 43,603	$ 48,656
Estimated future benefit payments 2017		4,700
Estimated future benefit payments 2018		4,200
Estimated future benefit payments 2019		3,700
Estimated future benefit payments 2020		4,000
Estimated future benefit payments 2021		3,100
Estimated future benefit payments, five years thereafter		13,700
Accumulated benefit obligation		$ 42,000	$ 45,500