Treasury Stock - Treasury Stock Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands				12 Months Ended
	Mar. 18, 2016	Sep. 16, 2015	May 15, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Treasury Stock [Roll Forward]
Beginning balance (shares)				4,499,655	2,395,049
Beginning balance				$ 88,756	$ 48,479
Shares repurchased				$ 54,601	$ 40,277	$ 48,479
Ending balance (shares)				6,788,817	4,499,655	2,395,049
Ending balance				$ 143,357	$ 88,756	$ 48,479
Average share price (usd per share)				$ 21.12	$ 19.73	$ 20.24
Repurchases on open market
Treasury Stock [Roll Forward]
Shares repurchased (shares)				2,289,162	1,204,606
Shares repurchased				$ 54,601	$ 25,787
Average share price (usd per share)				$ 23.85	$ 21.41
Repurchase from LSF8 in private transaction
Treasury Stock [Roll Forward]
Shares repurchased (shares)	900,000	1,007,500	913,200	0	900,000
Shares repurchased	$ 14,500	$ 20,000	$ 20,000	$ 0	$ 14,490
Average share price (usd per share)	$ 16.10	$ 19.85	$ 21.90	$ 0.00	$ 16.10