Capital Stock - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2008	Dec. 31, 2007
Equity, Class of Treasury Stock [Line Items]
Common stock available for issuance, Authorized	48,000,000	48,000,000
Preferred stock available for issuance	2,000,000	2,000,000
Stock repurchase program				$ 23,100,000	$ 5,000,000
Stock repurchase program expiration date	Sep. 22, 2017
Repurchase of common stock	199,053	0
Aggregate purchase price common stock	$ 1,286,000		$ 332,000
Remaining authorized repurchase amount	$ 7,400,000
Prior Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program expiration date	Sep. 21, 2018