Restricted Stock Units Activity (Detail) (Restricted stock units, USD $)	3 Months Ended
	Mar. 31, 2012 Year
Restricted stock units
Number of Units
Outstanding at beginning of period	34,738
Granted	39,237
Forfeited	0
Outstanding at end of period	73,975
Exercisable at end of period	0
Vested and expected to vest in the future at end of period	46,472
Weighted Average Remaining Contractual Life (in years)
Outstanding at end of period	3.24
Exercisable at end of period	0.00
Vested and expected to vest in the future at end of period	2.74
Aggregate Intrinsic Value
Outstanding at end of period	$ 6,187,269
Exercisable at end of period	0
Vested and expected to vest in the future at end of period	$ 3,886,902