Pension Plans and Other Postretirement Benefits (Details 3) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Total		$ 25,446	$ 27,667
Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total		12,402	13,720
Short-term Investments Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total		716	422
United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	[1]	9,836	10,844
International [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	[1]	2,492	2,681
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total		716	422
Level 1 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total		0	0
Level 1 [Member] | Short-term Investments Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total		716	422
Level 1 [Member] | United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	[1]	0	0
Level 1 [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	[1]	0	0
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total		24,730	27,245
Level 2 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total		12,402	13,720
Level 2 [Member] | Short-term Investments Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total		0	0
Level 2 [Member] | United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	[1]	9,836	10,844
Level 2 [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	[1]	2,492	2,681
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total		0	0
Level 3 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total		0	0
Level 3 [Member] | Short-term Investments Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total		0	0
Level 3 [Member] | United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	[1]	0	0
Level 3 [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	[1]	$ 0	$ 0

[1] None of the trust fund assets for the defined benefit pension plan have been invested in shares of HMEC’s common stock.