Employee Benefits (Fair Value Change in Investment in Real Estate) (Details) - Retirement Income Plan - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of prior year		$ 260,035		$ 272,939
Fair value of plan assets at end of year		269,766		260,035
Limited Partnership Interest in Real Estate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of prior year		8,588	[1],[2]	8,748
Unrealized gain (loss) in fair value		(822)		(160)
Sale of Land		(775)
Fair value of plan assets at end of year	[1],[2]	$ 6,991		$ 8,588

[1] In the first quarter of 2016, the Company implemented ASU 2015-07, Fair Value Measurement (Topic 820) which eliminates the requirement to categorize investments in the fair value hierarchy if the fair value is measured at NAV per share (or its equivalent) using the practical expedient in the FASB’s fair value measurement guidance. The fair value amounts presented in the table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the statement of financial position. ASU 2015-07 is effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years.

[2] This investment is a commercial real estate partnership that purchases land, develops limited infrastructure, and sells it for commercial development. The Company was restricted from selling its partnership interest during the life of the partnership, which spanned 7 years. Return on investment is realized as land is sold. The fair value of the limited partnership interest in real estate is based on the NAV of the partnership which reflects the appraised value of the land. The partnership term expired on June 30, 2016. Upon expiration, dissolution of the partnership commenced and, as a result, the general partner of the partnership is attempting to sell the remaining inventory as soon as possible at the highest pricing possible.