Changes in Shareholders' Equity - Changes in Shareholders' Equity (Parenthetical) (Detail) shares in Thousands	9 Months Ended
	Sep. 30, 2015 $ / shares shares
Issuance of common shares for stock options exercised | shares	2,851
Preferred stock dividends per share	$ 5.00
Common stock dividends per share	$ 0.12
Common Stock [Member]
Issuance of common shares for stock options exercised | shares	2,851
Additional Paid-in Capital [Member]
Issuance of common shares for stock options exercised | shares	2,851
Retained Earnings [Member]
Preferred stock dividends per share	$ 5.00
Common stock dividends per share	$ 0.12