Defined Benefit Retirement Plan (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 item	Mar. 31, 2014
Defined Benefit Retirement Plan
Number of officers for whom unfunded, non-qualified, defined benefit retirement plan is sponsored	3
Number of current officers for whom unfunded, non-qualified, defined benefit retirement plan is sponsored	2
Number of retired officers for whom unfunded, non-qualified, defined benefit retirement plan is sponsored	1
Benefits vesting period	25 years
Net periodic benefits costs, which include interest cost and amortization of net losses	$ 36	$ 32