Pension Plan and Postretirement Benefits Other Than Pension (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2011
Pension Plan and Postretirement Benefits Other than Pension
Amount of transfer between levels	$ 0	$ 0
Level 3
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	3,402	4,019
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	4,019	1,772
Purchases, issuances and settlements		1,900
Valuation change	(617)	347
Fair value of plan assets at end of year	3,402	4,019
Pension Benefits
Pension Plan and Postretirement Benefits Other than Pension
Amount of transfer between levels	0	0
Total fair value	175,548	170,430	103,404
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	170,430	133,911	103,404
Fair value of plan assets at end of year	175,548	170,430	103,404
Pension Benefits | Equity securities: Domestic
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	90,061	54,558
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	90,061	54,558
Pension Benefits | Equity securities: Foreign
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	29,351	67,889
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	29,351	67,889
Pension Benefits | Equity derivatives
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	116	471
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	116	471
Pension Benefits | Mortgage-backed securities
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	14	17
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	14	17
Pension Benefits | Corporate bonds
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	1,884	1,900
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	1,884	1,900
Pension Benefits | Private equity
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	1,518	2,119
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	1,518	2,119
Pension Benefits | Gold bullion
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	12,209	12,316
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	12,209	12,316
Pension Benefits | Total investment securities
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	135,153	139,270
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	135,153	139,270
Pension Benefits | Cash and other
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	40,395	31,160
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	40,395	31,160
Pension Benefits | Level 1 | Equity securities: Domestic
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	90,061	54,558
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	90,061	54,558
Pension Benefits | Level 1 | Equity securities: Foreign
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	29,351	67,889
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	29,351	67,889
Pension Benefits | Level 1 | Gold bullion
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	12,209	12,316
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	12,209	12,316
Pension Benefits | Level 1 | Total investment securities
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	131,621	134,763
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	131,621	134,763
Pension Benefits | Level 2 | Equity derivatives
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	116	471
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	116	471
Pension Benefits | Level 2 | Mortgage-backed securities
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	14	17
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	14	17
Pension Benefits | Level 2 | Total investment securities
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	130	488
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	130	488
Pension Benefits | Level 3 | Corporate bonds
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	1,884	1,900
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	1,884	1,900
Pension Benefits | Level 3 | Private equity
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	1,518	2,119
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	1,518	2,119
Pension Benefits | Level 3 | Total investment securities
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	3,402	4,019
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	$ 3,402	$ 4,019