Employee Benefits Plans (Details 6) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 89,727	$ 76,499	$ 71,207
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,775,417	1,832,490	1,612,927
Pension Benefits [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	63,346
Pension Benefits [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,685,690	1,692,645
Pension Benefits [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	89,727	76,499
Pension Benefits [Member] | Private equity and hedge funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	89,727	76,499
Pension Benefits [Member] | Private equity and hedge funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits [Member] | Private equity and hedge funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits [Member] | Private equity and hedge funds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	89,727	76,499
Pension Benefits [Member] | Equity securities [Member] | U.S. companies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		63,346
Pension Benefits [Member] | Equity securities [Member] | U.S. companies [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		63,346
Pension Benefits [Member] | Equity securities [Member] | U.S. companies [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Pension Benefits [Member] | Equity securities [Member] | U.S. companies [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Pension Benefits [Member] | Equity securities [Member] | U.S. mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	421,185	406,358
Pension Benefits [Member] | Equity securities [Member] | U.S. mutual funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits [Member] | Equity securities [Member] | U.S. mutual funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	421,185	406,358
Pension Benefits [Member] | Equity securities [Member] | U.S. mutual funds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits [Member] | Equity securities [Member] | Foreign mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	405,224	431,933
Pension Benefits [Member] | Equity securities [Member] | Foreign mutual funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits [Member] | Equity securities [Member] | Foreign mutual funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	405,224	431,933
Pension Benefits [Member] | Equity securities [Member] | Foreign mutual funds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits [Member] | Fixed income securities [Member] | Corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	70,999	59,917
Pension Benefits [Member] | Fixed income securities [Member] | Corporate bonds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits [Member] | Fixed income securities [Member] | Corporate bonds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	70,999	59,917
Pension Benefits [Member] | Fixed income securities [Member] | Corporate bonds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits [Member] | Fixed income securities [Member] | Mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	788,282	794,437
Pension Benefits [Member] | Fixed income securities [Member] | Mutual funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits [Member] | Fixed income securities [Member] | Mutual funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	788,282	794,437
Pension Benefits [Member] | Fixed income securities [Member] | Mutual funds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0