Pension Plan and Employee Benefits, Fair Value of Pension Plan Assets (Details) - Pension Benefits [Member] - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 338,128	$ 371,203
Investments Measured at Net Asset Value	42,362	38,770
Interest Accrual	3,042	2,830
Total net assets	383,532	412,803	$ 384,555
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,568	5,180
Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13,816	13,967
Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		968
Obligations of U.S. Government and U.S. Government Agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	48,792	49,942
Mutual funds, Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	47,801	55,005
Mutual funds, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22,853	25,096
Real estate funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17,890	18,792
Hedge Fund of Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,000
Corporate debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	182,408	202,253
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	84,470	95,036
Level 1 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13,816	13,967
Level 1 [Member] | Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		968
Level 1 [Member] | Obligations of U.S. Government and U.S. Government Agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Mutual funds, Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	47,801	55,005
Level 1 [Member] | Mutual funds, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22,853	25,096
Level 1 [Member] | Real estate funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Corporate debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	235,768	257,375
Level 2 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,568	5,180
Level 2 [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Level 2 [Member] | Obligations of U.S. Government and U.S. Government Agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	48,792	49,942
Level 2 [Member] | Mutual funds, Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Mutual funds, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Real estate funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Corporate debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	182,408	202,253
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17,890	18,792
Level 3 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Level 3 [Member] | Obligations of U.S. Government and U.S. Government Agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Mutual funds, Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Mutual funds, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Real estate funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17,890	18,792
Total net assets	17,890	18,792	$ 17,928
Level 3 [Member] | Corporate debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0