Outstanding and Weighted Average Common Shares - Additional Information (Detail) (USD $)	3 Months Ended												12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Out-of-the-money stock options													1,400,000	4,400,000	9,200,000
Cash dividends on common stock	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 1.00	$ 0.70	$ 0.40
Performance Share Units [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Out-of-the-money stock options															414,175