Components of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at the beginning of the period	$ 1,120,882
Other comprehensive (loss) income before reclassifications	(3,172)	$ (101,396)	$ (57,265)
Net losses (gains) reclassified from accumulated other comprehensive loss	(232)	161,240	(322)
Total other comprehensive (loss) income	(3,404)	59,844	(57,587)
Balance at the end of the period	1,551,113	1,120,882
Foreign Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at the beginning of the period	(2,676)	(6,028)	(4,500)
Other comprehensive (loss) income before reclassifications	(2,908)	3,352	(1,528)
Net losses (gains) reclassified from accumulated other comprehensive loss	0	0	0
Total other comprehensive (loss) income	(2,908)	3,352	(1,528)
Balance at the end of the period	(5,584)	(2,676)	(6,028)
Unrealized Net Gains (Losses) on Available for Sale Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at the beginning of the period	0	(56,420)	0
Other comprehensive (loss) income before reclassifications	0	(106,445)	(56,420)
Net losses (gains) reclassified from accumulated other comprehensive loss	0	162,865	0
Total other comprehensive (loss) income	0	56,420	(56,420)
Balance at the end of the period	0	0	(56,420)
Derivatives Qualifying as Cash Flow Hedges [Member] | Foreign Exchange Contract [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at the beginning of the period	691	619	258
Other comprehensive (loss) income before reclassifications	(264)	1,697	683
Net losses (gains) reclassified from accumulated other comprehensive loss	(232)	(1,625)	(322)
Total other comprehensive (loss) income	(496)	72	361
Balance at the end of the period	195	691	619
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at the beginning of the period	(1,985)	(61,829)	(4,242)
Balance at the end of the period	$ (5,389)	$ (1,985)	$ (61,829)