Employee Benefits (Fair Value Measurement Inputs) (Details) - USD ($)		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, Sales, Issuances, Settlements		$ 0		$ 0
Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Restriction Period To Sell Partnership Interest Minimum		5 years
Restriction Period To Sell Partnership Interest Maximum		7 years
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		260,035,000		272,939,000		$ 257,831,000
Cash and Cash Equivalents | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year		1,266,000		1,237,000
Common Collective Trusts | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]	250,181,000		262,954,000
Limited Partnership Interest in Real Estate | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year		8,588,000	[2]	8,748,000	[2]	$ 8,857,000
Fair Value, Inputs, Level 1 | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year		1,266,000		1,237,000
Fair Value, Inputs, Level 1 | Cash and Cash Equivalents | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year		1,266,000		1,237,000
Fair Value, Inputs, Level 1 | Common Collective Trusts | Retirement Income 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 1 | Limited Partnership Interest in Real Estate | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[2]	0		0
Fair Value, Inputs, Level 2 | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year		250,181,000		262,954,000
Fair Value, Inputs, Level 2 | Cash and Cash Equivalents | Retirement Income 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 | Common Collective Trusts | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]	250,181,000		262,954,000
Fair Value, Inputs, Level 2 | Limited Partnership Interest in Real Estate | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[2]	0		0
Fair Value, Inputs, Level 3 | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year		8,588,000		8,748,000
Fair Value, Inputs, Level 3 | Cash and Cash Equivalents | Retirement Income 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 | Common Collective Trusts | Retirement Income 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 | Limited Partnership Interest in Real Estate | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[2]	8,588,000		8,748,000
Common Collective Trusts | Equity Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]	144,279,000		149,839,000
Common Collective Trusts | Fixed Income Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]	103,877,000		113,115,000
Common Collective Trusts | Real Estate Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]	2,025,000
Common Collective Trusts | Fair Value, Inputs, Level 1 | Equity Funds | Retirement Income 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
Common Collective Trusts | Fair Value, Inputs, Level 1 | Fixed Income Funds | Retirement Income 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
Common Collective Trusts | Fair Value, Inputs, Level 1 | Real Estate Funds | Retirement Income 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
Common Collective Trusts | Fair Value, Inputs, Level 2 | Equity Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]	144,279,000		149,839,000
Common Collective Trusts | Fair Value, Inputs, Level 2 | Fixed Income Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]	103,877,000		113,115,000
Common Collective Trusts | Fair Value, Inputs, Level 2 | Real Estate Funds | Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets at end of year	[1]	2,025,000
Common Collective Trusts | Fair Value, Inputs, Level 3 | Equity Funds | Retirement Income 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
Common Collective Trusts | Fair Value, Inputs, Level 3 | Fixed Income Funds | Retirement Income 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
Common Collective Trusts | Fair Value, Inputs, Level 3 | Real Estate Funds | Retirement Income 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

[1] The Common Collective Trusts are invested in equity and fixed income securities, or a combination thereof. The investment objective of each trust is to produce returns in excess of, or commensurate with, its predefined index.

[2] This investment is a commercial real estate partnership that purchases land, develops limited infrastructure, and sells it for commercial development. The Company is restricted from selling its partnership interest during the life of the partnership which is generally 5-7 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.