Accumulated Other Comprehensive Income (Loss) - Summary of Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), Pre-Tax Amount	$ (1,700)	$ 685	$ (2,507)	$ 3,415
Other comprehensive income (loss), Tax (Expense) Benefit	0	(244)	0	(1,217)
Other comprehensive income (loss) before reclassification adjustments, After-Tax Amount	(2,035)	1,218	(2,585)	3,176
Other comprehensive income (loss), Reclassification adjustments, After-Tax Amount	335	(777)	78	(978)
Total other comprehensive (loss) income, net of tax	(1,700)	441	(2,507)	2,198
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	(2,202)	1,428	(2,356)	4,315
Other comprehensive income (loss), Reclassification adjustments, Pre-Tax Amount	335	(777)	78	(978)
Other comprehensive income (loss), Pre-Tax Amount	(1,867)	651	(2,278)	3,337
Other comprehensive income (loss) before reclassification adjustments, Tax (Expense) Benefit	0	(232)	0	(1,189)
Other comprehensive income (loss), Reclassification adjustments, Tax (Expense) Benefit	0	0	0	0
Other comprehensive income (loss), Tax (Expense) Benefit	0	(232)	0	(1,189)
Other comprehensive income (loss) before reclassification adjustments, After-Tax Amount	(2,202)	1,196	(2,356)	3,126
Other comprehensive income (loss), Reclassification adjustments, After-Tax Amount	335	(777)	78	(978)
Total other comprehensive (loss) income, net of tax	(1,867)	419	(2,278)	2,148
Unrealized Gains (Losses) on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassification adjustments, Pre-Tax Amount	167	34	(229)	78
Other comprehensive income (loss), Pre-Tax Amount	167	34	(229)	78
Other comprehensive income (loss) before reclassification adjustments, Tax (Expense) Benefit	0	(12)	0	(28)
Other comprehensive income (loss), Tax (Expense) Benefit	0	(12)	0	(28)
Other comprehensive income (loss) before reclassification adjustments, After-Tax Amount	167	22	(229)	50
Other comprehensive income (loss), Reclassification adjustments, After-Tax Amount	0	0	0	0
Total other comprehensive (loss) income, net of tax	$ 167	$ 22	$ (229)	$ 50