Other short-term borrowings (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Short-term Debt [Line Items]
Advances with the FHLB paying interest at maturity, at fixed rates ranging from 0.37% to 0.46%	$ 1,225,000	$ 635,000
Others	1,200	1,200
Total other short-term borrowings	$ 1,226,200	$ 636,200