Reconciliations of Equity - Reconciliations of Total Equity (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Reconciliations of total equity
Beginning Balance	$ 1,214,522	$ 1,189,913	$ 1,216,490	$ 1,166,065
Issuance of common stock under incentive compensation plan	101	402	966	1,916
Stock-based and deferred compensation	2,357	2,077	(283)	(535)
Net income	9,521	12,684	23,414	28,826
Other comprehensive income (loss)	(25,634)	18,178	(31,298)	35,142
Cash dividends paid:
Common stock	(8,431)	(8,157)	(16,853)	(16,317)
Ending Balance	1,192,436	1,215,097	1,192,436	1,215,097
Common Stock [Member]
Reconciliations of total equity
Beginning Balance	27,125	26,958	27,006	26,841
Issuance of common stock under incentive compensation plan	2	7	23	33
Stock-based and deferred compensation	15	13	113	104
Cash dividends paid:
Ending Balance	27,142	26,978	27,142	26,978
Additional Paid-in Capital [Member]
Reconciliations of total equity
Beginning Balance	248,337	239,585	247,032	237,202
Issuance of common stock under incentive compensation plan	99	395	943	1,883
Stock-based and deferred compensation	2,509	2,235	2,970	3,130
Cash dividends paid:
Ending Balance	250,945	242,215	250,945	242,215
Common Treasury Stock [Member]
Reconciliations of total equity
Beginning Balance	(187,611)	(184,194)	(184,412)	(180,596)
Stock-based and deferred compensation	(167)	(171)	(3,366)	(3,769)
Cash dividends paid:
Ending Balance	(187,778)	(184,365)	(187,778)	(184,365)
Accumulated Other Comprehensive Income (Loss) [Member]
Reconciliations of total equity
Beginning Balance	(136,266)	(150,548)	(130,602)	(167,512)
Other comprehensive income (loss)	(25,634)	18,178	(31,298)	35,142
Cash dividends paid:
Ending Balance	(161,900)	(132,370)	(161,900)	(132,370)
Retained Earnings [Member]
Reconciliations of total equity
Beginning Balance	1,262,937	1,258,112	1,257,466	1,250,130
Net income	9,521	12,684	23,414	28,826
Cash dividends paid:
Common stock	(8,431)	(8,157)	(16,853)	(16,317)
Ending Balance	$ 1,264,027	$ 1,262,639	$ 1,264,027	$ 1,262,639