Comprehensive Income and Accumulated Other Comprehensive Income - Schedule of Changes in Accumulated Other Comprehensive Income (AOCI) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 430,215	$ 409,762	$ 425,423
Net current period other comprehensive income (loss)	8,808	13,043	(4,243)
Ending Balance	438,816	430,215	409,762
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	12,211	(832)	3,612
Other comprehensive income (loss) before reclassification	9,538	12,379	(4,551)
Amounts reclassified from accumulated other comprehensive income (loss)	(730)	664	308
Net current period other comprehensive income (loss)	8,808	13,043	(4,243)
Ending Balance	21,019	12,211	(832)
Accumulated Other Comprehensive Income (Loss) [Member] | ASU 2016-01 [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			(615)
Accumulated Other Comprehensive Income (Loss) [Member] | ASU 2018-02 [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			414
Accumulated Other Comprehensive Income (Loss) [Member] | ASU 2016-01 [Member] | ASU 2016-01 [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			(615)
Accumulated Other Comprehensive Income (Loss) [Member] | ASU 2016-01 [Member] | ASU 2018-02 [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			414
Accumulated Other Comprehensive Income (Loss) [Member] | Cumulative Effect, Period of Adoption, Adjusted Balance [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Adjusted beginning balance	$ 12,211	$ (832)	$ 3,411