Note Loans (Composition of loans held-in-portfolio-covered loans and past due status) (Detail) - USD ($) $ in Thousands	Mar. 31, 2018		Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans covered under loss-sharing agreements with the FDIC	$ 514,611		$ 517,274
Covered loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	116,861		82,764
Current	397,750		434,510
Loans covered under loss-sharing agreements with the FDIC	514,611	[1]	517,274	[2]
Covered loans | Past Due 30 To 59 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	45,430		17,158
Covered loans | Past Due 60 To 89 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,753		5,600
Covered loans | Past Due 90 Days or More
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	68,678		60,006
Covered loans | Mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	114,604		81,111
Current	386,079		421,818
Loans covered under loss-sharing agreements with the FDIC	500,683		502,929
Covered loans | Mortgages | Past Due 30 To 59 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	44,199		16,640
Covered loans | Mortgages | Past Due 60 To 89 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,753		5,453
Covered loans | Mortgages | Past Due 90 Days or More
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	67,652		59,018
Covered loans | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,257		1,653
Current	11,671		12,692
Loans covered under loss-sharing agreements with the FDIC	13,928		14,345
Covered loans | Consumer | Past Due 30 To 59 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,231		518
Covered loans | Consumer | Past Due 60 To 89 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0		147
Covered loans | Consumer | Past Due 90 Days or More
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 1,026		$ 988

[1] Includes $268 million pledged to secure credit facilities at the FHLB which are not permitted to sell or repledge the collateral.

[2] Includes $279 million pledged to secure credit facilities at the FHLB which are not permitted to sell or repledge the collateral.