Stock Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended				3 Months Ended	12 Months Ended					3 Months Ended		3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2006	Dec. 31, 2008 20% of the shares issued	Dec. 31, 2007 20% of the shares issued	Dec. 31, 2006 20% of the shares issued	Mar. 31, 2013 25% of the shares issued	Dec. 31, 2012 25% of the shares issued	Dec. 31, 2011 25% of the shares issued	Dec. 31, 2009 Non-Employee Directors	Dec. 31, 2008 Non-Employee Directors	Dec. 31, 2007 Non-Employee Directors	Mar. 31, 2013 Stock Options	Jun. 01, 2006 Stock Options	Mar. 31, 2013 Stock Options Maximum	Mar. 31, 2013 Performance Shares	Dec. 31, 2006 Performance Shares
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Common stock reserved for issuance														8,000,000
Options granted vesting period													4 years		10 years	5 years
Restricted stock-based compensation expense	$ 1,011,000	$ 856,000
Incentive restricted stock issued			16,536	33,000	66,000	57,500	0	108,828	91,364	12,224	80,676	14,464					153,500
Shares granted exercise price				$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Percentage of shares vested				20.00%	20.00%	20.00%	25.00%	25.00%	25.00%	25.00%	25.00%	25.00%
Aggregate fair value of shares vested	$ 0	$ 0