Accumulated Other Comprehensive Loss - Activity within Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 764,597
Other comprehensive income	5,659	$ 6,051
Ending balance	979,022
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(77,356)	(94,100)
Ending balance	$ (71,697)	$ (88,049)