Common Stock - Additional Information (Detail)	1 Months Ended					2 Months Ended	12 Months Ended
	Oct. 31, 2015 USD ($) $ / shares shares	Nov. 30, 2014 USD ($) $ / shares shares	Oct. 31, 2014 USD ($) $ / shares shares	May. 31, 2014 USD ($) $ / shares shares	Apr. 30, 2014 USD ($) $ / shares shares	Nov. 30, 2014 USD ($) $ / shares	Dec. 31, 2015 USD ($) Vote $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($)	May. 31, 2015 USD ($) shares
Class of Stock [Line Items]
Shares authorized at incorporation | shares							150,000,000
Common stock, shares authorized | shares							130,000,000	130,000,000
Common stock, par value (usd per share) | $ / shares							$ 0.0001	$ 0.0001
Preferred stock, shares authorized | shares							20,000,000	20,000,000
Preferred stock, par value (usd per share) | $ / shares							$ 0.0001	$ 0.0001
Common stock, number of votes per share | Vote							1
Minimum percent of combined voting power							75.00%
Minimum percent of shareholders for affirmative vote consent							75.00%
Common stock sold, shares | shares	6,272,727		2,000,000
Common stock sold, price (usd per share) | $ / shares	$ 5.50		$ 17.50
Total costs	$ 280,000		$ 3,000,000				$ 283,000	$ 0	$ 3,112,000
Proceeds from issuance of common stock, net of issuance costs	32,100,000		32,600,000			$ 32,900,000	32,189,000	87,899,000	$ 0
Underwriting discounts and commission	2,100,000
Net offering proceeds			32,000,000
Offering expenses			$ 511,000
Maximum aggregate offering price	165,500,000									$ 200,000,000.0
Maximum number of shares to be sold under shelf registration | shares										2,500,000.0
Maximum aggregate offering price under the shelf registration										$ 75,000,000.0
Value of stock issued during the period	$ 34,500,000						$ 32,150,000	32,853,000
IPO [Member]
Class of Stock [Line Items]
Common stock sold, shares | shares					4,500,000
Common stock sold, price (usd per share) | $ / shares					$ 12.00
Proceeds from IPO					$ 50,200,000
Estimated offering expenses					5,800,000
Total costs					9,600,000
Proceeds from issuance of common stock, net of issuance costs					$ 44,400,000
Value of stock issued during the period								$ 51,933,000
Over-Allotment Option [Member]
Class of Stock [Line Items]
Common stock sold, shares | shares	818,181	50,000		675,000
Common stock sold, price (usd per share) | $ / shares		$ 17.50		$ 12.00		$ 17.50
Proceeds from IPO				$ 7,500,000
Proceeds from issuance of common stock, net of issuance costs		$ 814,000
Underwriting discounts and commission				567,000
Net offering proceeds				$ 51,900,000