Comprehensive Income and Accumulated Other Comprehensive Income - Schedule of Changes in Accumulated Other Comprehensive Income (AOCI) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 456,150
Ending Balance	467,101
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(492)	$ 2,587
Other comprehensive income before reclassification	978	3,033
Amounts reclassified from accumulated other comprehensive income	(26)	(240)
Net current period other comprehensive income	952	2,793
Ending Balance	$ 460	$ 5,380