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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, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 425,423	$ 456,150	$ 453,981
Net current period other comprehensive income (loss)	(4,243)	4,104	(3,079)
Ending Balance	409,762	425,423	456,150
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	3,612	(492)	2,587
Adjusted beginning balance	3,411	(492)	2,587
Other comprehensive income (loss) before reclassification	(4,551)	4,823	(3,231)
Amounts reclassified from accumulated other comprehensive income (loss)	308	(719)	152
Net current period other comprehensive income (loss)	(4,243)	4,104	(3,079)
Ending Balance	(832)	$ 3,612	$ (492)
Accumulated Other Comprehensive Income (Loss) [Member] | ASU 2016-01 [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Impact of adoption of ASU	(615)
Accumulated Other Comprehensive Income (Loss) [Member] | ASU 2018-02 [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Impact of adoption of ASU	$ 414

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