Noninterest Income and Expense - Components of Other Noninterest Income (Detail) - USD ($) $ in Thousands	3 Months Ended						6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule Of Other Noninterest Income And Expense [Line Items]
Commissions on sale of non-deposit investment products	$ 810				$ 705		$ 1,686	$ 1,312
Gain on sale of loans	666				777		1,292	1,687
Increase in cash value of life insurance	656				626		1,264	1,311
Gain on sale of foreclosed assets	17				153		388	271
Lease brokerage income	200				161		328	367
Sale of customer checks	138				94		239	198
Change in indemnification asset					711			490
Life insurance proceeds in excess of cash value								108
Loss on disposal of fixed assets	(41)				(28)		(54)	(28)
Loss on marketable equity securities	(23)						(70)
Other	523				232		807	511
Total other noninterest income	2,946				3,431		5,880	6,227
Total noninterest income	12,174	$ 12,290	$ 12,478	$ 12,930	12,910	$ 11,703	24,464	24,613
Service Charges on Deposit Accounts [Member]
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees	3,613				4,323		7,392	7,942
ATM and Interchange Fees [Member]
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees	4,510				4,248		8,745	8,263
Other Service Fees [Member]
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees	630				839		1,344	1,604
Mortgage Banking Service Fees [Member]
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees	511				526		1,028	1,047
Change in Value of Mortgage Servicing Rights [Member]
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees	(36)				(457)		75	(470)
Financial Service [Member]
Schedule Of Other Noninterest Income And Expense [Line Items]
Total service charges and fees	$ 9,228				$ 9,479		$ 18,584	$ 18,386