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Selected Financial Data - Summary of Selected Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands | 3 Months Ended | 12 Months Ended
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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
Quarterly Financial Information Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Interest income | $ 53,353 | $ 53,669 | $ 52,611 | $ 43,916 | $ 41,381 | $ 40,605 | $ 39,872 | $ 38,665 | $ 203,548 | $ 160,523 | $ 153,756
Interest expense | 4,468 | 4,073 | 3,800 | 3,657 | 3,315 | 3,076 | 3,017 | 3,074 | 15,997 | 12,481 | 14,563
Provision for loan losses | 3,915 | 3,206 | 2,059 | 1,207 | 1,106 | 1,454 | (1,134) | 289 | 10,388 | 1,715 | 8,311
Net Interest Income After Provision for Loan Losses | 44,970 | 46,390 | 46,752 | 39,052 | 36,960 | 36,075 | 37,989 | 35,302 | 177,163 | 146,327 | 130,882
Security gains, net | 0 | 0 | (34) | 0 | 0 | 0 | 40 | 1 |  |  |
Noninterest income | 13,084 | 12,481 | 13,417 | 12,084 | 11,220 | 11,931 | 11,731 | 11,415 | 51,033 | 46,338 | 51,527
Noninterest expense | 33,817 | 33,829 | 35,449 | 33,621 | 29,720 | 28,440 | 30,165 | 28,914 | 136,717 | 117,240 | 117,392
Income before taxes | 24,237 | 25,042 | 24,686 | 17,515 | 18,460 | 19,566 | 19,595 | 17,804 |  |  |
Provision for income taxes | 6,814 | 6,407 | 6,498 | 4,680 | 3,963 | 4,906 | 4,875 | 3,771 | 24,398 | 17,515 | 14,478
Net Income Available to Common Shareholders | $ 17,423 | $ 18,635 | $ 18,188 | $ 12,835 | $ 14,497 | $ 14,660 | $ 14,720 | $ 14,033 | $ 66,801 | $ 57,745 | $ 50,392
Common earnings per share-diluted (in USD per share) | $ 0.50 | $ 0.54 | $ 0.52 | $ 0.41 | $ 0.49 | $ 0.49 | $ 0.49 | $ 0.47 | $ 1.98 | $ 1.95 | $ 1.70
Dividends declared per common share (in USD per share) | 0.19 | 0.18 | 0.18 | 0.18 | 0.18 | 0.17 | 0.17 | 0.16 | $ 0.73 | $ 0.68 | $ 0.61
Common book value (in USD per share) | $ 22.76 | $ 22.63 | $ 22.15 | $ 21.91 | $ 20.42 | $ 20.33 | $ 20.04 | $ 19.64 |  |  |

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