Fair Values of Assets and Liabilities - Schedule of Changes in Level 3 Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$ 4,870	$ 18,094	$ 4,366	$ 27,459
Total gains or losses included in earnings	0	5,262	(47)	8,102
Total gains or losses included in other comprehensive income	0	(4,647)	0	(118)
Purchases	112	5	663	154
Issuances	0	0	0	0
Sales	0	(12,289)	0	(12,289)
Settlements	0	(2,458)	0	(19,341)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0	0	0	0
Balance, end of period	4,982	3,967	4,982	3,967
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	0	0	0
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period		14,132		23,646
Total gains or losses included in earnings		5,262		8,102
Total gains or losses included in other comprehensive income		(4,647)		(118)
Purchases		0		0
Issuances		0		0
Sales		(12,289)		(12,289)
Settlements		(2,458)		(19,341)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0		0
Balance, end of period		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0		0
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	1,670	1,670	1,670	1,670
Total gains or losses included in earnings	0	0	0	0
Total gains or losses included in other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0	0	0	0
Balance, end of period	1,670	1,670	1,670	1,670
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	0	0	0
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	3,200	2,292	2,696	2,143
Total gains or losses included in earnings	0	0	(47)	0
Total gains or losses included in other comprehensive income	0	0	0	0
Purchases	112	5	663	154
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0	0	0	0
Balance, end of period	3,312	2,297	3,312	2,297
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	$ 0	$ 0	$ 0	$ 0