Allowance for Credit Losses - Progression of Allowance for Credit Losses Including Allowance for Loan Losses and Reserve for Lending-Related Commitments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Receivables [Abstract]
Balance of allowance for loan losses at beginning of period				$ 76,703				$ 76,627	$ 76,703	$ 76,627	$ 72,771
Provision for loan losses	$ 5,867	$ 5,033	$ 5,417	$ 4,996	$ 5,823	$ 4,808	$ 6,204	$ 5,178	21,313	22,013	28,406
Financing receivable allowance and provisions for credit losses									98,016	98,640	101,177
Loans charged off									(29,110)	(28,606)	(32,863)
Recoveries									8,151	6,669	8,313
Net charge-offs									(20,959)	(21,937)	(24,550)
Balance of allowance for loan losses at end of period	77,057				76,703				77,057	76,703	76,627
Reserve for lending-related commitments	1,733				1,389				1,733	1,389	679
Balance of allowance for credit losses at end of period	$ 78,790				$ 78,092				$ 78,790	$ 78,092	$ 77,306