Summary of Quarterly Results of Operations (Unaudited) - Result of Operations (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Loans:                      
Discount accretion PCI - cash basis $ 302 $ 445 $ 404 $ 172 $ 107 $ 290 $ 69 $ 203      
Discount accretion PCI - other 1,392 1,090 907 1,274 919 822 811 984      
Discount accretion PNCI 573 1,590 822 1,348 796 402 624 379      
All other loan interest income 32,571 30,689 29,886 28,371 28,914 23,466 22,929 22,172      
Total loan interest income 34,838 33,814 32,019 31,165 30,736 24,980 24,433 23,738      
Debt securities, dividends and interest bearing cash at banks (not FTE) 7,652 7,518 7,848 6,560 5,671 4,151 3,985 3,421      
Total interest and dividend income 42,490 41,332 39,867 37,725 36,407 29,131 28,418 27,159 $ 161,414 $ 121,115 $ 106,560
Interest expense 1,349 1,339 1,346 1,382 1,437 1,082 1,075 1,087 5,416 4,681 4,696
Net interest income 41,141 39,993 38,521 36,343 34,970 28,049 27,343 26,072 155,998 116,434 101,864
(Benefit from) provision for loan losses (908) (866) (633) 197 (1,421) (2,977) 1,708 (1,355) (2,210) (4,045) (715)
Net interest income after provision for loan losses 42,049 40,859 39,154 36,146 36,391 31,026 25,635 27,427 158,208 120,479 102,579
Noninterest income 11,445 11,642 12,080 10,180 9,755 8,589 7,877 8,295 45,347 34,516 36,829
Noninterest expense 34,684 31,439 32,436 32,282 36,566 25,380 25,116 23,317 130,841 110,379 93,604
Income before income taxes 18,810 21,062 18,798 14,044 9,580 14,235 8,396 12,405 72,714 44,616 45,804
Income tax expense 7,388 8,368 7,432 5,708 3,930 6,001 3,537 5,040 28,896 18,508 18,405
Net income $ 11,422 $ 12,694 $ 11,366 $ 8,336 $ 5,650 $ 8,234 $ 4,859 $ 7,365 $ 43,818 $ 26,108 $ 27,399
Per common share:                      
Net income (diluted) $ 0.50 $ 0.55 $ 0.49 $ 0.36 $ 0.25 $ 0.50 $ 0.30 $ 0.45 $ 1.91 $ 1.46 $ 1.69
Dividends $ 0.15 $ 0.13 $ 0.13 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11