Employee Benefits (Fair Value Measurements- Other Postretirement Benefits) (Details) - USD ($)			12 Months Ended
		Jun. 30, 2016	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value, Assets, Level 1 to Level 2 Transfers, Description			no		no
Fair Value, Assets, Level 2 to Level 1 Transfers, Description			no		no
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, Sales, Issuances, Settlements			$ 0		$ 0
Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Restriction Period To Sell Partnership Interest Maximum			7 years
Fair Value, Assets, Level 1 to Level 2 Transfers, Description			no		no
Fair Value, Assets, Level 2 to Level 1 Transfers, Description			no		no
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, Sales, Issuances, Settlements			$ 0		$ 0
Fair value of plan assets at end of year			39,115,000		38,090,000		$ 41,358,000
Limited Partnership expiration date		Jun. 30, 2016
Institutional Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		37,804,000		36,480,000
Limited Partnership Interest in Real Estate | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			1,311,000	[2],[3]	1,610,000	[2],[3]	$ 1,640,000
Fair Value, Inputs, Level 1 | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			37,804,000		36,480,000
Fair Value, Inputs, Level 1 | Institutional Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		37,804,000		36,480,000
Fair Value, Inputs, Level 2 | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			0		0
Fair Value, Inputs, Level 2 | Institutional Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Fair Value, Inputs, Level 3 | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year			0		0
Fair Value, Inputs, Level 3 | Institutional Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Institutional Funds | Equity Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		26,133,000		24,881,000
Institutional Funds | Fixed Income Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		11,671,000		11,599,000
Institutional Funds | Fair Value, Inputs, Level 1 | Equity Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		26,133,000		24,881,000
Institutional Funds | Fair Value, Inputs, Level 1 | Fixed Income Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		11,671,000		11,599,000
Institutional Funds | Fair Value, Inputs, Level 2 | Equity Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Institutional Funds | Fair Value, Inputs, Level 2 | Fixed Income Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Institutional Funds | Fair Value, Inputs, Level 3 | Equity Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		0		0
Institutional Funds | Fair Value, Inputs, Level 3 | Fixed Income Funds | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]		$ 0		$ 0

[1] The institutional funds are invested in equity or fixed income securities, or a combination thereof. The investment objective of each fund is to produce returns in excess of, or commensurate with, its predefined index.

[2] 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.

[3] 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 of 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.