Stock Based Compensation - Additional Information (Detail) (Restricted Units, USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation units, granted in period	30,200
Vesting period of restricted stock unit award	4 years
Long Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	$ 333,000	$ 147,000
Board of Directors Chairman
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation units, granted in period	6,000
Board of Directors Chairman | Long Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	$ 536,000	$ 371,000
Board of Directors Chairman | Third anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage	50.00%
Board of Directors Chairman | Fourth anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage	50.00%