Summary of Net Gains (Losses) Included in Consolidated Statements of Operations for Changes in Fair Value of Derivatives and Periodic Net Interest Settlements Under Derivatives (Detail) - Interest Rate Swap - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Net loss for changes in fair value and net settlements of derivatives	$ 4,800	$ 5,400	$ 5,500
Net Realized Investment Gains (Losses)
Derivative Instruments, Gain (Loss) [Line Items]
Net loss for changes in fair value and net settlements of derivatives	$ (1,110)	$ (6,988)	$ (20,836)