Equity Based compensation - Summary of Stock Options and Restricted Stock Activity (Detail) (USD $)	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 2011 Plan [Member]	Dec. 31, 2012 2011 Plan [Member]	Mar. 31, 2013 2011 Plan [Member] 2011 Grants [Member]	Mar. 31, 2011 2011 Plan [Member] 2011 Grants [Member]	Mar. 31, 2013 2011 Plan [Member] 2012 Grants [Member]	Mar. 31, 2012 2011 Plan [Member] 2012 Grants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of restricted stock	2,782	62,500				89,751		8,020
Weighted- average grant date fair value per share						$ 10.48		$ 6.50
Stock options outstanding						383,251
Weighted- average exercise price						$ 10.51
Shares available for issuance under the 2011 Plan	1,724		18,978	500,000
Grants					(473,002)		(8,020)
Remaining shares available for issuance at March 31, 2013	1,724		18,978	500,000