Equity Based compensation - Summary of Stock Options and Restricted Stock Activity (Detail) (USD $)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of restricted stock	11,189	62,500
Stock options outstanding	11,953	18,703	30,003	36,803
2011 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share available for issuance under the 2011 Plan	18,978	500,000
Remaining shares available for issuance at December 31, 2012	18,978	500,000
2011 Plan [Member] | 2011 Grants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of restricted stock		89,751
Weighted-average grant date fair value per share		10.48
Stock options outstanding		383,251
Weighted average exercise price		10.51
2011 Grants	(473,002)
2011 Plan [Member] | 2012 Grants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of restricted stock	8,020
Weighted-average grant date fair value per share	6.50
2011 Grants	(8,020)