Pension Plan and Postretirement Benefits Other Than Pension (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2012
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	3,402	4,019
Sales	(3,432)
Valuation change	30	(617)
Fair value of plan assets at end of year		3,402
Pension Benefits
Pension Plan and Postretirement Benefits Other than Pension
Amount of transfer between levels	0	0
Total fair value	175,548	170,430	$ 133,911
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	175,548	170,430
Fair value of plan assets at end of year	173,885	175,548
Pension Benefits | Equity securities: Domestic
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	90,061	90,061
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	90,061
Fair value of plan assets at end of year	92,037	90,061
Pension Benefits | Equity securities: Foreign
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	29,351	29,351
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	29,351
Fair value of plan assets at end of year	25,822	29,351
Pension Benefits | Equity derivatives
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	116	116
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	116
Fair value of plan assets at end of year	280	116
Pension Benefits | Mortgage-backed securities
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	14	14
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	14
Fair value of plan assets at end of year	11	14
Pension Benefits | U.S. treasuries
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	8,113
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	8,113
Pension Benefits | Corporate bonds
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	1,884	1,884
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	1,884
Fair value of plan assets at end of year		1,884
Pension Benefits | Private equity
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	1,518	1,518
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	1,518
Fair value of plan assets at end of year		1,518
Pension Benefits | Gold bullion
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	12,209	12,209
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	12,209
Fair value of plan assets at end of year	5,226	12,209
Pension Benefits | Total investment securities
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	135,153	135,153
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	135,153
Fair value of plan assets at end of year	131,489	135,153
Pension Benefits | Cash and other
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	40,395	40,395
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	40,395
Fair value of plan assets at end of year	42,396	40,395
Pension Benefits | Level 1 | Equity securities: Domestic
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	90,061	90,061
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	90,061
Fair value of plan assets at end of year	92,037	90,061
Pension Benefits | Level 1 | Equity securities: Foreign
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	29,351	29,351
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	29,351
Fair value of plan assets at end of year	25,822	29,351
Pension Benefits | Level 1 | Gold bullion
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	12,209	12,209
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	12,209
Fair value of plan assets at end of year	5,226	12,209
Pension Benefits | Level 1 | Total investment securities
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	131,621	131,621
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	131,621
Fair value of plan assets at end of year	123,085	131,621
Pension Benefits | Level 2 | Equity derivatives
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	116	116
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	116
Fair value of plan assets at end of year	280	116
Pension Benefits | Level 2 | Mortgage-backed securities
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	14	14
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	14
Fair value of plan assets at end of year	11	14
Pension Benefits | Level 2 | U.S. treasuries
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	8,113
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at end of year	8,113
Pension Benefits | Level 2 | Total investment securities
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	130	130
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	130
Fair value of plan assets at end of year	8,404	130
Pension Benefits | Level 3 | Corporate bonds
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	1,884	1,884
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	1,884
Fair value of plan assets at end of year		1,884
Pension Benefits | Level 3 | Private equity
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	1,518	1,518
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	1,518
Fair value of plan assets at end of year		1,518
Pension Benefits | Level 3 | Total investment securities
Pension Plan and Postretirement Benefits Other than Pension
Total fair value	3,402	3,402
Summary of the activity of plan assets categorized as Level 3 during the period
Fair value of plan assets at beginning of year	$ 3,402
Fair value of plan assets at end of year		$ 3,402