Earnings Per Share - Common Shares Related to Stock Options and RSUs Excluded from Calculated Diluted Net Income Per Share (Parenthetical) (Detail)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Performance based options, bearing right to acquire common stock	155,000	110,000
Total Performance based options and restricted stock units, bearing right to acquire common stock	199,000
Restricted Stock Units (RSUs) [Member]
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Restricted stock units, bearing right to acquire common stock	44,000	400,000