Comprehensive Income and Accumulated Other Comprehensive Income - Schedule of Changes in Accumulated Other Comprehensive Income (AOCI) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 430,405	$ 432,068	$ 409,762	$ 425,423
Change in deferred tax valuation allowance	198
Ending Balance	449,443	445,391	449,443	445,391
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	4,962	(2,236)	(832)	3,612
Other comprehensive income (loss) before reclassification	5,001	(449)	10,889	(5,863)
Amounts reclassified from accumulated other comprehensive income	(21)	602	83	168
Change in deferred tax valuation allowance	198
Net current period other comprehensive income (loss)	5,178	153	10,972	(5,695)
Ending Balance	$ 10,140	$ (2,083)	$ 10,140	$ (2,083)