Calculation of Net Income per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2013	Jun. 30, 2012
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Net income	$ 12,162		$ 7,207		$ 22,720	$ 15,683
Basic:
Basic weighted average EPS shares	24,965	24,965	24,393	24,393	24,938	24,098
Basic net income per share	$ 0.49		$ 0.30		$ 0.91	$ 0.65
Diluted:
Basic weighted average EPS shares	24,965	24,965	24,393	24,393	24,938	24,098
Dilutive common stock equivalents	44		31		68	83
Dilutive EPS shares	25,009		24,424		25,006	24,181
Diluted net income per share	$ 0.49		$ 0.30		$ 0.91	$ 0.65
Anti-dilutive shares	211		527		224	507