Stock Based Compensation - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted stock [Member]
Stock Option Activity Under The Company's Incentive Plans [Line Items]
Expense related to incentive compensation plan	$ 2.2	$ 1.7	$ 1.8
2005 Executive Incentive Compensation Plan [Member]
Stock Option Activity Under The Company's Incentive Plans [Line Items]
Number of common stock expected to be granted	8,125,000
Expiration period	10 years
2005 Executive Incentive Compensation Plan [Member] | Restricted stock [Member]
Stock Option Activity Under The Company's Incentive Plans [Line Items]
Restricted stock shares granted	404,793	756,492	500,468
2005 Executive Incentive Compensation Plan [Member] | Minimum [Member] | Restricted stock [Member]
Stock Option Activity Under The Company's Incentive Plans [Line Items]
Restricted stock vesting period	3 years
2005 Executive Incentive Compensation Plan [Member] | Maximum [Member] | Restricted stock [Member]
Stock Option Activity Under The Company's Incentive Plans [Line Items]
Restricted stock vesting period	5 years
2005 Non-Employee Directors Restricted Stock Plan [Member]
Stock Option Activity Under The Company's Incentive Plans [Line Items]
Number of common stock expected to be granted	575,000
Expiration period	10 years
Restricted stock shares granted	27,696	53,274	90,820
Expiration date	Mar. 31, 2025