Employee Retirement Plans (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current target allocations
Target allocations (as a percent)	100.00%	100.00%
Contributory retirement (401(k)) savings plans
Company contributions	$ 147	$ 147	$ 149
Corson Plan
Employee retirement plans
Unfunded projected benefit obligation	290	487
Comprehensive loss, net of tax benefit	64	149
Comprehensive loss, tax benefit	36	85
Contributions by the entity	151	18	194
Expected contribution by the entity in 2013	83
Number of major components of plan assets	2
Pension plan assets at the fair value
Fair value of assets	1,892	1,664	1,815
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	2,151	2,048
Interest cost	89	104	108
Actuarial loss on plan assets	54	115
Benefits paid	(112)	(116)
Projected benefit obligation at end of year	2,182	2,151	2,048
Change in plan assets:
Fair value of plan assets at beginning of year	1,664	1,815
Employer contribution	151	18	194
Actual gain (loss) on plan assets	189	(53)
Benefits paid	(112)	(116)
Fair value of plan assets at end of year	1,892	1,664	1,815
Funded status
Underfunded status	(290)	(487)
Accumulated Benefit Obligation
Accumulated benefit obligation	2,182	2,151
Net liability recognized on the consolidated balance sheets
Accrued benefit cost	290	487
Weighted-average assumptions used in the measurement of benefit obligation
Discount rate (as a percent)	3.64%	4.25%
Expected long-term return on plan assets (as a percent)	7.00%	7.75%
Components of the net periodic benefit cost
Interest cost	89	104	108
Expected return on plan assets	(119)	(137)	(126)
Amortization of net actuarial loss	84	71	71
Net periodic benefit cost	54	38	53
Expected benefit payments
2013	119
2014	125
2015	124
2016	125
2017	130
2018-2022	707
Corson Plan | Level 1
Pension plan assets at the fair value
Fair value of assets	1,892	1,664
Change in plan assets:
Fair value of plan assets at end of year	1,892	1,664
Corson Plan | Equity securities and funds
Current target allocations
Target allocations, minimum (as a percent)	50.00%
Target allocations, maximum (as a percent)	70.00%
Target allocations (as a percent)	28.90%	47.00%
Corson Plan | Equity securities and funds | Level 1
Pension plan assets at the fair value
Fair value of assets	547	782
Change in plan assets:
Fair value of plan assets at end of year	547	782
Corson Plan | Institutional bond funds
Current target allocations
Target allocations, minimum (as a percent)	25.00%
Target allocations, maximum (as a percent)	50.00%
Target allocations (as a percent)	58.20%	39.60%
Corson Plan | Institutional bond funds | Level 1
Pension plan assets at the fair value
Fair value of assets	1,101	660
Change in plan assets:
Fair value of plan assets at end of year	1,101	660
Corson Plan | Other investments
Current target allocations
Target allocations, minimum (as a percent)	0.00%
Target allocations, maximum (as a percent)	15.00%
Target allocations (as a percent)	5.90%	10.20%
Corson Plan | Other investments | Level 1
Pension plan assets at the fair value
Fair value of assets	112	170
Change in plan assets:
Fair value of plan assets at end of year	112	170
Corson Plan | Cash and cash equivalents
Current target allocations
Target allocations, minimum (as a percent)	0.00%
Target allocations, maximum (as a percent)	10.00%
Target allocations (as a percent)	7.00%	3.20%
Corson Plan | Cash and cash equivalents | Level 1
Pension plan assets at the fair value
Fair value of assets	132	52
Change in plan assets:
Fair value of plan assets at end of year	$ 132	$ 52