Income Taxes - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2018	Dec. 31, 2017 USD ($) State	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Income Tax Disclosure [Line Items]
Tax bad debt reserve	$ 137,121,000		$ 137,121,000
Income taxes attributable to gains or losses on bank investment securities			7,195,000	$ 11,925,000	$ 0
Alternative minimum tax expense recognized for gains or losses on bank investment securities			$ 0	$ 0	$ 0
Federal income tax rate			35.00%
Estimated incremental income tax expense related to Tax Act	$ 85,000,000
Number of state and local jurisdictions where company files income tax returns | State			40
ASU 2016-09 [Member]
Income Tax Disclosure [Line Items]
New accounting pronouncement or change in accounting principle effect of adoption change in income tax expense (benefit)			$ (22,000,000)
Scenario Forecast [Member]
Income Tax Disclosure [Line Items]
Federal income tax rate		21.00%