Debt (Details Textual) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Senior Notes 2015 [Member]
Debt (Textual) [Abstract]
Senior Notes	6.05%	6.05%
Senior Notes 2015 [Member] | Senior Note 6.05 % [Member]
Debt (Textual) [Abstract]
Unaccrued discount	$ 31	$ 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	79	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%