Common Stock - Summary of Stock Option Transactions (Detail) - Stock Options [Member] $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares
Schedule Of Stock Options [Line Items]
Outstanding balance at Dec. 31, 2014, Number of Shares	840
Granted, Number of Shares	0
Exercised, Number of Shares	(580)
Cancelled, Number of Shares	(6)
Outstanding balance at Dec. 31, 2015, Number of Shares	254
Exercisable at Dec. 31, 2015, Number of Shares	254
Available for future grant at Dec. 31, 2015, Number of Shares	2,429
Outstanding balance at Dec. 31, 2014, Weighted Avg. Option Price (per share) | $ / shares	$ 16.32
Granted, Weighted Avg. Option Price | $ / shares	0.00
Exercised, Weighted Avg. Option Price | $ / shares	16.30
Cancelled, Weighted Avg. Option Price | $ / shares	18.87
Outstanding balance at Dec. 31, 2015, Weighted Avg. Option Price (per share) | $ / shares	16.30
Exercisable at Dec. 31, 2015, Weighted Avg. Option Price | $ / shares	$ 16.30
Outstanding balance at Dec. 31, 2015, Weighted Avg. Remaining Contractual Term	1 year
Exercisable at Dec. 31, 2015, Weighted Avg. Remaining Contractual Term	1 year
Outstanding balance at Dec. 31, 2015, Aggregate Intrinsic Value | $	$ 2.6
Exercisable at Dec. 31, 2015, Aggregate Intrinsic Value | $	$ 2.6