Summary of Gross Amounts, Amounts Offset and net Amounts of Repurchase Agreement and Reverse Repurchase Agreement (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Repurchase Agreements:
Gross amounts -reverse repurchase agreements	$ 0	$ 0
Amounts offset - reverse repurchase agreement	0	0
Netted amounts -reverse repurchase	0	0
Gross amounts -repurchase agreement	54,448,141	56,230,860
Amounts offset -repurchase agreement	0	0
Netted amounts -repurchase agreement	$ 54,448,141	$ 56,230,860	[1]

[1] Derived from the audited consolidated financial statements at December 31, 2015.