Stockholders' Equity - Common Stock Purchased Including Purchase of Common Stock for Tax Withholdings (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended			36 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015
Equity, Class of Treasury Stock [Line Items]
Total Number of Shares Purchased (shares)	189,438	502,942	177,330	247,797	263,772	0	0	0	0	0	108,459	0	1,117,507	263,772	108,459	1,489,738
Average Price Paid Per Share (usd per share)	$ 16.87	$ 16.52	$ 16.93	$ 17.31	$ 16.36	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 12.92	$ 0.00	$ 16.82	$ 16.36	$ 12.92	$ 16.46
Publicly Announced Plans or Programs
Equity, Class of Treasury Stock [Line Items]
Total Number of Shares Purchased (shares)	189,438,000	502,942,000	177,330,000	27,467,000	263,772,000	0	0	0	0	0	0	0	897,177,000	263,772,000	0	1,160,949,000
Approximate Dollar Value of Shares That May Yet Be Purchased Under the Publicly Announced Plans or Programs	$ 0	$ 3,224	$ 11,531	$ 14,536	$ 10,685	$ 15,000	$ 15,000	$ 15,000	$ 16,964	$ 16,964	$ 16,964	$ 16,964