Non-interest Income and Expense - Components of Other Noninterest Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees									$ 37,981	$ 40,417	$ 38,460
Commissions on sale of non-deposit investment products									2,989	2,877	3,151
Increase in cash value of life insurance									2,949	3,029	2,718
Gain on sale of loans									9,122	3,282	2,371
Lease brokerage income									668	878	678
Sale of customer checks									414	529	449
Gain on sale of investment securities									7	110	207
Gain (loss) on marketable equity securities									64	86	(64)
Other									1,000	2,312	1,091
Total other noninterest income									17,213	13,103	10,601
Total noninterest income	$ 16,580	$ 15,137	$ 11,657	$ 11,820	$ 14,186	$ 14,108	$ 13,423	$ 11,803	55,194	53,520	49,061
Debit and ATM and interchange fees
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees									21,660	20,639	18,249
Service charges on deposit accounts
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees									13,944	16,657	15,467
Other service fees
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees									3,156	3,015	2,852
Mortgage banking service fees
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees									1,855	1,917	2,038
Change in value of mortgage loan servicing rights
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees									$ (2,634)	$ (1,811)	$ (146)