Loans - Additional Information (Detail)						3 Months Ended			9 Months Ended			12 Months Ended
		Sep. 30, 2017 USD ($)		Sep. 29, 2017 USD ($)	Jul. 28, 2017 USD ($)	Sep. 30, 2017 USD ($) Investment		Sep. 30, 2016 USD ($) Investment	Sep. 30, 2017 USD ($) Investment		Sep. 30, 2016 USD ($) Investment	Dec. 31, 2016 USD ($)
Financing Receivable, Recorded Investment [Line Items]
Outstanding loans to Executive officers, directors, principal shareholders, related interest and parties		$ 58,700,000				$ 58,700,000			$ 58,700,000			$ 91,800,000
Non-Covered Loans		37,480,704,000				37,480,704,000			37,480,704,000			37,356,201,000
Loans held for sale		104,938,000				104,938,000			104,938,000			409,152,000
Delinquent loans selectively extended to certain borrowers, rate reductions, forbearance of arrears, and extension of maturity dates						$ 16,272,000		$ 1,273,000	$ 33,315,000		$ 11,491,000
Number of loans modified as TDRs | Investment						24		2	58		8
Covered loans		0				$ 0			$ 0			1,698,133,000
Accretable		0
Provision for (recovery of) losses						44,585,000		$ (55,000)	34,316,000		$ 664,000
FDIC indemnification expense								1,000,000	19,000,000		4,800,000
Freedom Mortgage Corporation
Financing Receivable, Recorded Investment [Line Items]
Mortgage servicing rights asset				$ 208,800,000
Loans held for sale				20,500,000,000
Gain on sale of business				7,400,000
Proceeds from sale of business				$ 226,600,000
Am Trust Bank and Desert Hills Bank
Financing Receivable, Recorded Investment [Line Items]
Total loans, net												2,100,000,000
Purchased Credit-Impaired Loans
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans												5,762,000
Purchased credit-impaired loans outstanding		0				0			0			7,000,000
One-to-four family
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		413,235,000				413,235,000			413,235,000			381,081,000
Delinquent loans selectively extended to certain borrowers, rate reductions, forbearance of arrears, and extension of maturity dates									$ 990,000		$ 628,000
Number of loans modified as TDRs | Investment									4		3
One-to-four family | Cerberus Capital Management, L. P.
Financing Receivable, Recorded Investment [Line Items]
Gain on sale of business					$ 74,600,000
Proceeds from sale of business					$ 1,900,000,000
Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		1,982,143,000				1,982,143,000			$ 1,982,143,000			1,900,445,000	[1]
Delinquent loans selectively extended to certain borrowers, rate reductions, forbearance of arrears, and extension of maturity dates						$ 7,620,000		$ 1,273,000	$ 23,673,000		$ 2,560,000
Number of loans modified as TDRs | Investment						22		2	52		4
Commercial and Industrial | Payment Default
Financing Receivable, Recorded Investment [Line Items]
Number of loans modified as TDRs | Investment									6
Loan modified as TDRs subsequently defaulted									$ 1,400,000
Principal shareholders
Financing Receivable, Recorded Investment [Line Items]
Outstanding loans to Executive officers, directors, principal shareholders, related interest and parties		0				$ 0			0			0
Financing Receivable Troubled Debt Restructurings Rate Reductions
Financing Receivable, Recorded Investment [Line Items]
Delinquent loans selectively extended to certain borrowers, rate reductions, forbearance of arrears, and extension of maturity dates									41,500,000
Financing Receivable Troubled Debt Restructurings Forbearance of Arrears
Financing Receivable, Recorded Investment [Line Items]
Delinquent loans selectively extended to certain borrowers, rate reductions, forbearance of arrears, and extension of maturity dates									1,800,000
Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Mortgage loans on real estate, foreclosures									0			78,600,000
Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Accretable									72,842,000
Current												1,500,000,000
Provision for (recovery of) losses								$ (1,289,000)	(23,701,000)		$ (6,035,000)
Covered Loans | Performing Financial Instruments | Financing Receivable Recorded Investment 30 to 89 days past due
Financing Receivable, Recorded Investment [Line Items]
Total Past Due												22,600,000
Covered Loans | Performing Financial Instruments | Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Total Past Due												131,500,000
Non-Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total Past Due		74,123,000				74,123,000			74,123,000			66,852,000
Current		37,406,581,000				37,406,581,000			37,406,581,000			37,283,587,000
Provision for (recovery of) losses						44,585,000		$ 1,234,000	58,017,000		$ 6,699,000
Non-Covered Loans | One-to-four family
Financing Receivable, Recorded Investment [Line Items]
Total Past Due		2,855,000				2,855,000			2,855,000			12,523,000
Current		410,380,000				410,380,000			$ 410,380,000			368,558,000
Non-Covered Loans | One-to-four family | Payment Default
Financing Receivable, Recorded Investment [Line Items]
Number of loans modified as TDRs | Investment									2
Loan modified as TDRs subsequently defaulted									$ 497,000,000,000
Non-Covered Loans | Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	[3]	48,059,000	[2]			48,059,000	[2]		48,059,000	[2]		23,685,000	[4]
Current	[3]	$ 1,934,084,000	[2]			$ 1,934,084,000	[2]		$ 1,934,084,000	[2]		1,876,760,000	[4]
Non-Covered Loans | Loans 90 Days Or More Past Due | Purchased Credit-Impaired Loans
Financing Receivable, Recorded Investment [Line Items]
Total Past Due												$ 869,000

[1] Includes lease financing receivables, all of which were classified as "pass."

[2] Includes $3.4 million and $43.4 million of taxi medallion-related loans that were 30 to 89 days past due and 90 days or more past due, respectively.

[3] Includes lease financing receivables, all of which were current.

[4] Includes $6.8 million and $15.2 million of taxi medallion loans that were 30 to 89 days past due and 90 days or more past due, respectively.