Employee Benefits Plans (Details 6) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 100,631	$ 89,727	$ 76,499
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,647,286	1,775,417	$ 1,832,490
Pension Plans | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,546,655	1,685,690
Pension Plans | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	100,631	89,727
Pension Plans | Private equity and hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	100,631	89,727
Pension Plans | Private equity and hedge funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans | Private equity and hedge funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans | Private equity and hedge funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	100,631	89,727
Pension Plans | Equity securities: | U.S. common collective trusts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	387,123	421,185
Pension Plans | Equity securities: | U.S. common collective trusts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans | Equity securities: | U.S. common collective trusts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	387,123	421,185
Pension Plans | Equity securities: | U.S. common collective trusts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans | Equity securities: | Foreign common collective trusts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	374,858	405,224
Pension Plans | Equity securities: | Foreign common collective trusts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans | Equity securities: | Foreign common collective trusts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	374,858	405,224
Pension Plans | Equity securities: | Foreign common collective trusts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans | Fixed income securities: | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	64,834	70,999
Pension Plans | Fixed income securities: | Corporate bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans | Fixed income securities: | Corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	64,834	70,999
Pension Plans | Fixed income securities: | Corporate bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans | Fixed income securities: | Common collective trusts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	719,840	788,282
Pension Plans | Fixed income securities: | Common collective trusts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans | Fixed income securities: | Common collective trusts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	719,840	788,282
Pension Plans | Fixed income securities: | Common collective trusts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0