Capital Management - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Oct. 31, 2016
Equity [Abstract]
Share repurchase program, new limit amount									$ 25,000,000
Shares repurchased under the program			0
Shares repurchased	1,258,250	1,258,250	1,258,250	1,258,250
Shares repurchased, value	$ 22,370,000	$ 22,370,000	$ 22,370,000	$ 22,370,000
Shares repurchased, average price			$ 17.78
Quarterly dividend per share	$ 0.22	$ 0.20	0.22	$ 0.20	$ 0.18	$ 0.15	$ 0.12	$ 0.08
Extraordinary dividends declared per share	$ 3.50	$ 3.50	$ 3.50	$ 3.50	$ 3.25	$ 3.00	$ 1.50	$ 0