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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			$ 453,981
Ending Balance	$ 509,743		509,743
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	8,309	$ 2,052	2,587	$ 2,810
Other comprehensive income (loss) before reclassification	(1,589)	1,400	4,286	(188)
Amounts reclassified from accumulated other comprehensive income	(124)	(92)	(277)	738
Net current period other comprehensive income (loss)	(1,713)	1,308	4,009	550
Ending Balance	$ 6,596	$ 3,360	$ 6,596	$ 3,360