Shares Repurchased Under Stock Repurchase Plan (Detail) - USD ($) $ in Thousands	3 Months Ended		4 Months Ended	12 Months Ended	168 Months Ended
	Dec. 31, 2016	Jul. 16, 2016	Apr. 23, 2016	Dec. 31, 2016	Dec. 31, 2016
Equity [Abstract]
Total Number of Shares Purchased	128	932,380	5,959,814	6,892,322	67,800
Total Cost of Shares Purchased	$ 2	$ 18,000	$ 108,298	$ 126,300	$ 630,400