Rollforward of Financial Instruments Classified in Level Three of Valuation Hierarchy (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Interest rate lock commitments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Beginning Balance	$ 982	$ 2,526
Total Realized/Unrealized (Losses)/Gains Recorded in (Loss)/ Income	(982)	(1,544)
Total Realized/Unrealized (Losses)/Gain Recorded in Comprehensive (Loss) Income	0	0
Transfers to/(from) level 3	0	0
Fair Value, Ending Balance		982
Change in Unrealized (Losses)/Gains Related to Instruments Held		982
Mortgage servicing rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Beginning Balance	228,099	243,389
Total Realized/Unrealized (Losses)/Gains Recorded in (Loss)/ Income	(20,076)	(27,453)
Total Realized/Unrealized (Losses)/Gain Recorded in Comprehensive (Loss) Income	0	0
Issuances	18,054	45,588
Settlements	(223,348)	(33,425)
Transfers to/(from) level 3	0	0
Fair Value, Ending Balance	2,729	228,099
Change in Unrealized (Losses)/Gains Related to Instruments Held	$ (222)	$ (27,453)