Noninterest Income and Expense - Components of Other Noninterest Income (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
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees									$ 40,417	$ 38,460	$ 37,423
Commissions on sale of non-deposit investment products									2,877	3,151	2,729
Increase in cash value of life insurance									3,029	2,718	2,685
Gain on sale of loans									3,282	2,371	3,109
Lease brokerage income									878	678	782
Sale of customer checks									529	449	372
Gain on sale of investment securities									110	207	961
Gain (loss) on marketable equity securities									86	(64)	0
Other									2,312	1,091	1,391
Total other noninterest income									13,103	10,601	12,029
Total noninterest income	$ 14,186	$ 14,108	$ 13,423	$ 11,803	$ 12,634	$ 12,186	$ 12,174	$ 12,290	53,520	49,061	49,452
ATM and interchange fees
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees									20,639	18,249	16,727
Service charges on deposit accounts
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees									16,657	15,467	16,056
Other service fees
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees									3,015	2,852	3,282
Mortgage banking service fees
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees									1,917	2,038	2,076
Change in value of mortgage loan servicing rights
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees									$ (1,811)	$ (146)	$ (718)