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Selected Quarterly Financial Data (unaudited) - Schedule of Selected Quarterly Statements of Income Data (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]                      
Revenues $ 114,025 $ 101,287 $ 98,227 $ 119,508 $ 87,810 $ 77,325 $ 73,880 $ 90,126 $ 433,047 $ 329,141 $ 224,653
Operating income 19,434 11,437 9,089 38,665 12,681 582 16,004 28,704 $ 78,625 $ 57,971 $ 34,435
Net income $ 12,905 $ 14,067 $ 14,221 $ 25,614 $ 8,633 $ 6,198 $ 10,421 $ 18,588      
Earnings per share, basic $ 0.22 $ 0.24 $ 0.24 $ 0.44 $ 0.15 $ 0.11 $ 0.18 $ 0.32 $ 1.15 $ 0.76 $ 0.37
Earnings per share, diluted $ 0.22 $ 0.24 $ 0.24 $ 0.43 $ 0.15 $ 0.10 $ 0.18 $ 0.31 $ 1.13 $ 0.74 $ 0.36
Weighted average shares outstanding:                      
Basic 58,100,141 58,003,222 57,898,914 57,307,187 57,652,531 57,819,734 57,591,556 57,132,909 57,839,155 57,550,204 56,495,170
Diluted 58,850,271 58,873,502 58,816,442 58,525,980 58,882,966 58,907,281 58,697,229 58,362,040 58,790,019 58,968,099 57,919,700