Earnings Per Share - Restricted Stock Awards and Share Repurchases (Detail) $ / shares in Units, $ in Thousands, shares in Millions	3 Months Ended			12 Months Ended
	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($) $ / shares shares	Mar. 31, 2014 USD ($) stockholder $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares
Repurchases of common stock
Repurchase and retirement of common stock | $				$ 50,261	$ 37,593	$ 3,025
Restricted Shares
Repurchases of common stock
Repurchased and retired shares | shares				0.2	0.1	0.2
Weighted average market price of shares repurchased and retired (in dollars per share) | $ / shares				$ 20.11	$ 15.53	$ 17.64
Common shares
Repurchases of common stock
Repurchased and retired shares | shares		3.0	2.5
Weighted average market price of shares repurchased and retired (in dollars per share) | $ / shares			$ 14.50
Number of stockholders participating in a share repurchase and retirement transaction | stockholder			1
Price paid per share for repurchased common stock | $ / shares		$ 15.60
Repurchase and retirement of common stock | $		$ 46,800	$ 35,500
Repurchase authorization | $	$ 75,000
Share repurchase program, period for repurchases	12 months