Share-Based Compensation - Additional Information (Detail) - USD ($)			12 Months Ended
	May 20, 2015	May 01, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 11, 2016	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (in shares)			55,112	75,456	77,369		142,000
Outstanding, Weighted average exercise price (in dollars per share)			$ 14.00	$ 14.00	$ 14.00		$ 14.00
Options exercises in period, intrinsic value			$ 200,000
Outstanding, exercisable, vested or expected to vest, intrinsic value			9,200,000	$ 7,700,000	$ 3,000,000
Compensation expense			2,800,000	$ 2,100,000	$ 700,000
Unrecognized compensation expense related to non-vested restricted stock			3,800,000
Employee stock purchase program, offering period		12 months
Employee contribution to ESPP through payroll deduction, maximum amount per employee (percent)		10.00%
Employee contribution to ESPP through payroll deduction, maximum amount per employee		$ 10,000
Purchase price of shares on closing price under ESPP (as a percent)		85.00%
ESPP expense			$ 100,000
Restricted stock awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unearned compensation expense, weighted average remaining period			2 years 2 months 20 days
Minimum [Member] | Performance restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of PRSUs earned						0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock purchase program, shares	600,000
Maximum | Performance restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of PRSUs earned						200.00%
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock purchase program, shares			20,342	10,873