Short-Term Borrowings - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt Disclosure [Abstract]
Weighted average interest rates on short-term borrowings during year	0.39%	0.43%	0.53%
Weighted average interest rates on short-term borrowings at period end	0.37%	0.41%	0.47%