Mortgage banking activities (Detail) - Mortgage Banking Activities [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Mortgage Servicing Fees Excluding Fair Value	$ 14,689	$ 10,558	$ 26,937	$ 21,306
Mortgage Servicing Rights MSR Impairment Recovery	(1,917)	(7,740)	(6,846)	(15,836)
Servicing Fees Net	12,772	2,818	20,091	5,470
Net gain on sale of loans, including valuation adjustments on loans held-for-sale	8,022	8,189	15,302	15,365
Unrealized Gain (Loss) on Derivatives	42	22	59	(738)
Gain (Loss) on Sale of Derivatives	489	(7,241)	(1,275)	(12,631)
Trading Gains (Losses)	531	(7,219)	(1,216)	(13,369)
Mortgage banking activities	$ 21,325	$ 3,788	$ 34,177	$ 7,466