Debt (Details Textual) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Current Unsecured Bank Credit Facility [Member]
Debt (Textual) [Abstract]
Unsecured borrowings	$ 150,000
Interest rate variable spread percentage	1.25%
Variable commitment fee unused portion	0.15%
Line of Credit Facility, Expiration Date	Oct. 06, 2015
Line of Credit Facility, Interest Rate at Period End	1.40%
Previous Unsecured Bank Credit Facility [Member]
Debt (Textual) [Abstract]
Line of Credit Facility, Expiration Date	Dec. 19, 2011
Senior Notes 2015 [Member]
Debt (Textual) [Abstract]
Senior Notes	6.05%	6.05%
Aggregate principal amount	75,000
Senior Notes 2015 [Member] | Senior Note 6.05 % [Member]
Debt (Textual) [Abstract]
Unaccrued discount	24	38
Aggregate principal amount	75,000	75,000
Maturity date of Senior note	Jun. 15, 2015	Jun. 15, 2015
Imputed rate	6.10%	6.10%
Senior Notes 2016 [Member]
Debt (Textual) [Abstract]
Senior Notes	6.85%	6.85%
Senior Notes 2016 [Member] | Senior Note 6.85 % [Member]
Debt (Textual) [Abstract]
Unaccrued discount	69	88
Aggregate principal amount	125,000	125,000
Maturity date of Senior note	Apr. 15, 2016	Apr. 15, 2016
Imputed rate	6.90%	6.90%
HMEC’s Bank Credit Facility [Member] | Current Unsecured Bank Credit Facility [Member]
Debt (Textual) [Abstract]
Current borrowing under the Current Bank Credit Facility	$ 38,000
Line of Credit Facility, Expiration Date	Jul. 30, 2019
HMEC’s Bank Credit Facility [Member] | Previous Unsecured Bank Credit Facility [Member]
Debt (Textual) [Abstract]
Line of Credit Facility, Expiration Date	Oct. 06, 2015