Summary Selected Quarterly Financial Data - Summary of Selected Consolidated Quarterly Financial Data (unaudited) (Detail) - USD ($) $ / shares in Units, $ in Thousands |
3 Months Ended | 12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2016 |
Sep. 30, 2016 |
Jun. 30, 2016 |
Mar. 31, 2016 |
Dec. 31, 2015 |
Sep. 30, 2015 |
Jun. 30, 2015 |
Mar. 31, 2015 |
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
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| Quarterly Financial Information Disclosure [Abstract] | |||||||||||
| Total revenues | $ 83,446 | $ 77,427 | $ 87,821 | $ 77,401 | $ 80,975 | $ 74,753 | $ 82,811 | $ 75,187 | $ 326,095 | $ 313,726 | $ 312,062 |
| Income (loss) from operations | 9,038 | 7,552 | 11,472 | 2,712 | 4,108 | 5,341 | 10,093 | (715) | 30,774 | 18,827 | 18,213 |
| Net income (loss) | $ 5,790 | $ 3,112 | $ 7,460 | $ 1,289 | $ 2,020 | $ 4,450 | $ 5,750 | $ (224) | $ 17,651 | $ 11,996 | $ 10,865 |
| Basic income (loss) per common share | $ 0.32 | $ 0.17 | $ 0.42 | $ 0.07 | $ 0.11 | $ 0.25 | $ 0.32 | $ (0.01) | $ 0.98 | $ 0.67 | $ 0.58 |
| Diluted income (loss) per common share | $ 0.31 | $ 0.17 | $ 0.41 | $ 0.07 | $ 0.11 | $ 0.25 | $ 0.31 | $ (0.01) | $ 0.97 | $ 0.66 | $ 0.57 |