Share Repurchase Plan - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	May 27, 2015	Oct. 23, 2013
Equity, Class of Treasury Stock [Line Items]
Share Repurchase Plan, Shares repurchased during period, shares	0	66,000	608,757
Shares Repurchase Plan, Share repurchased during period, cost	$ 0	$ 1,400	$ 12,000
Stock Repurchase Plan, Remaining number of shares authorized to be repurchased	1,014,246
Shares, Outstanding	29,334,859
Treasury Stock, Value	$ 43,533	$ 44,906
2013 Plan [Member]
Equity, Class of Treasury Stock [Line Items]
Share Repurchase Plan, Number of shares authorized to be repurchased				1,000,000
Share Repurchase Plan, Percentage of shares authorized to be repurchased				5.00%	5.00%
2013 Plan [Member] | Maximum [Member]
Equity, Class of Treasury Stock [Line Items]
Share Repurchase Plan, Number of shares authorized to be repurchased					800,000