Components of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at the beginning of the period			$ 1,232,466
Total other comprehensive income (loss)	$ 131,854	$ (19,196)	59,494	$ (18,185)
Balance at the end of the period	1,124,565		1,124,565
Foreign Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at the beginning of the period			(6,028)	(4,500)
Other comprehensive income (loss) before reclassifications			2,347	(199)
Net losses (gains) reclassified from accumulated other comprehensive loss			0	0
Total other comprehensive income (loss)			2,347	(199)
Balance at the end of the period	(3,681)	(4,699)	(3,681)	(4,699)
Unrealized Net Gains (Losses) on Available for Sale Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at the beginning of the period			(56,420)	0
Other comprehensive income (loss) before reclassifications			(85,652)	(18,115)
Net losses (gains) reclassified from accumulated other comprehensive loss			142,165	0
Total other comprehensive income (loss)			56,513	(18,115)
Balance at the end of the period	93	(18,115)	93	(18,115)
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			619	258
Other comprehensive income (loss) before reclassifications			1,411	121
Net losses (gains) reclassified from accumulated other comprehensive loss			(777)	8
Total other comprehensive income (loss)			634	129
Balance at the end of the period	1,253	387	1,253	387
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at the beginning of the period			(61,829)	(4,242)
Other comprehensive income (loss) before reclassifications			(81,894)	(18,193)
Net losses (gains) reclassified from accumulated other comprehensive loss			141,388	8
Total other comprehensive income (loss)			59,494	(18,185)
Balance at the end of the period	$ (2,335)	$ (22,427)	$ (2,335)	$ (22,427)