Accumulated Other Comprehensive Income (Loss) - Summary of Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), Pre-Tax Amount	$ (807)	$ 2,730
Other comprehensive income (loss), Tax (Expense) Benefit	0	(973)
Other comprehensive income (loss) before reclassification adjustments, After-Tax Amount	(550)	1,958
Other comprehensive income (loss), Reclassification adjustments, After-Tax Amount	(257)	(201)
Total other comprehensive (loss) income, net of tax	(807)	1,757
Unrealized Gains (Losses) on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassification adjustments, Pre-Tax Amount	(154)	2,887
Other comprehensive income (loss), Reclassification adjustments, Pre-Tax Amount	(257)	(201)
Other comprehensive income (loss), Pre-Tax Amount	(411)	2,686
Other comprehensive income (loss) before reclassification adjustments, Tax (Expense) Benefit	0	(957)
Other comprehensive income (loss), Reclassification adjustments, Tax (Expense) Benefit	0	0
Other comprehensive income (loss), Tax (Expense) Benefit	0	(957)
Other comprehensive income (loss) before reclassification adjustments, After-Tax Amount	(154)	1,930
Other comprehensive income (loss), Reclassification adjustments, After-Tax Amount	(257)	(201)
Total other comprehensive (loss) income, net of tax	(411)	1,729
Unrealized Gains (Losses) on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassification adjustments, Pre-Tax Amount	(396)	44
Other comprehensive income (loss), Pre-Tax Amount	(396)	44
Other comprehensive income (loss) before reclassification adjustments, Tax (Expense) Benefit	0	(16)
Other comprehensive income (loss), Tax (Expense) Benefit	0	(16)
Other comprehensive income (loss) before reclassification adjustments, After-Tax Amount	(396)	28
Other comprehensive income (loss), Reclassification adjustments, After-Tax Amount	0	0
Total other comprehensive (loss) income, net of tax	$ (396)	$ 28