Comprehensive Income and Accumulated Other Comprehensive Income - Schedule of Changes in Accumulated Other Comprehensive Income (AOCI) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 449,443	$ 445,391	$ 409,762	$ 425,423
Ending Balance	468,729	458,996	468,729	458,996
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	10,140	(2,083)	(832)	3,612
Other comprehensive income (loss) before reclassification	2,467	(2,143)	12,844	(7,964)
Amounts reclassified from accumulated other comprehensive income	8	25	603	151
Net current period other comprehensive income (loss)	2,475	(2,118)	13,447	(7,813)
Ending Balance	$ 12,615	$ (4,201)	$ 12,615	$ (4,201)