Employee Benefit Plans - Fair Value Measurements (Details) - Pension - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Fair Value	$ 50,970	$ 55,546	$ 341,905
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair Value	13,774	15,149
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair Value	37,196	40,397
Domestic equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value	19,952	22,883
Domestic equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair Value	3,781	4,557
Domestic equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair Value	16,171	18,326
International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value	12,349	12,765
International equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair Value	6,062	6,277
International equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair Value	6,287	6,488
Domestic fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value	13,654	14,643
Domestic fixed income securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair Value	0	0
Domestic fixed income securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair Value	13,654	14,643
International fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value	2,348	2,428
International fixed income securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair Value	2,348	2,428
International fixed income securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair Value	0	0
Real estate fund
Defined Benefit Plan Disclosure [Line Items]
Fair Value	1,583	1,887
Real estate fund | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair Value	1,583	1,887
Real estate fund | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair Value	0	0
Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair Value	1,084	940
Short-term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair Value	0	0
Short-term investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair Value	$ 1,084	$ 940