Noninterest Income and Expense - Components of Other Noninterest Income (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017
Income Statement [Abstract]
Service charges on deposit accounts	$ 3,779				$ 3,619
ATM and interchange fees	4,235				4,015
Other service fees	714				765
Mortgage banking service fees	517				521
Change in value of mortgage servicing rights	111				(13)
Total service charges and fees	9,356				8,907
Commissions on sale of non-deposit investment products	876				607
Gain on sale of loans	626				910
Increase in cash value of life insurance	608				685
Gain on sale of foreclosed assets	371				118
Lease brokerage income	128				206
Sale of customer checks	101				104
Change in indemnification asset					(221)
Life insurance proceeds in excess of cash value					107
Loss on disposal of fixed assets	(13)
Loss on marketable equity securities	(47)
Other	284				280
Total other noninterest income	2,934				2,796
Total noninterest income	$ 12,290	$ 12,478	$ 12,930	$ 12,910	$ 11,703