Summary of Significant Accounting Policies - Shares Used in Computation of Basic and Diluted Per Share Information (Detail) - shares	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Weighted average shares outstanding:
Weighted average number of shares outstanding for basic per share calculation (in shares)	30,777,556	30,750,227	30,497,501	17,789,863	17,749,872	17,740,818	17,728,567	17,643,463	27,498,351	17,715,992	17,559,477
Effect of dilutive potential shares:
Options (in shares)									0	0	863
Nonvested restricted stock (in shares)									275,045	245,026	122,480
Adjusted weighted average shares for diluted per share calculation (in shares)	31,142,061	31,083,815	30,742,293	18,039,345	18,043,297	18,010,522	17,964,387	17,817,880	27,773,396	17,961,018	17,682,820
Antidilutive shares (in shares)									46,002	0	219,855