Impairment of Investment Securities - Additional Information (Detail)		12 Months Ended
		Dec. 31, 2019 USD ($) Security	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Number of securities in an unrealized loss positions | Security		36
Corporate/Mortgage-Backed Securities, Amortized cost		$ 896,495,000	$ 924,054,000
Securities available for sale		902,292,000	909,247,000
Other than-temporary impairment charge	[1]	0	9,164,000	$ 0
Other investments		15,100,000	30,500,000
Equity Securities, FV-NI		1,700,000
Equity Securities, FV-NI, Gain (Loss)		0
Threshold Percentage of Value Decline in Equity Securities to be considered Other than Temporary Impairment			0	0
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Debt and Equity Securities, FV-NI [Line Items]
Other than-temporary impairment charge		$ 0	0	$ 0
Obligations of U.S. Government-Sponsored Enterprises [Member]
Debt and Equity Securities, FV-NI [Line Items]
Total unrealized losses		90.00%
Corporate Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Corporate/Mortgage-Backed Securities, Amortized cost		$ 22,919,000	20,912,000
Securities available for sale		$ 23,962,000	21,012,000
Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage - Backed Securities - Residential [Member]
Debt and Equity Securities, FV-NI [Line Items]
Total unrealized losses		10.00%
Number of securities in an unrealized loss positions | Security		25
Corporate/Mortgage-Backed Securities, Amortized cost		$ 660,777,000	686,906,000
Securities available for sale		$ 661,947,000	$ 673,361,000

[1] Represents the increase in cash flows recognized either as principal payments or interest income during the period.