Pension Plan and Employee Benefits, Fair Value of Pension Plan Assets (Details) (Pension Benefits [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 409,973	$ 381,771
Interest Accrual	2,830	2,784
Total net assets	412,803	384,555	344,041
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,180	5,942
Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13,967	17,918
Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	968	939
Obligations of U.S. Government and U.S. Government Agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	49,942	41,413
Mutual funds, Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	55,005	54,609
Mutual funds, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25,096	26,254
Common/collective trust fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	37,542	42,078
Real estate funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18,792	17,928
Hedge Fund of Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,228	1,740
Corporate debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	202,253	172,950
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	95,036	99,720
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	13,967	17,918
Level 1 [Member] | Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	968	939
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	55,005	54,609
Level 1 [Member] | Mutual funds, International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25,096	26,254
Level 1 [Member] | Common/collective trust fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Real estate funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Hedge Fund of 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	294,917	262,383
Level 2 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,180	5,942
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	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	49,942	41,413
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] | Common/collective trust fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	37,542	42,078
Level 2 [Member] | Real estate funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Hedge Fund of 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	202,253	172,950
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20,020	19,668
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	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] | Common/collective trust fund [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	18,792	17,928
Level 3 [Member] | Hedge Fund of Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,228	1,740
Level 3 [Member] | Corporate debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0