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Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Consolidated Statements of Comprehensive Income [Abstract] |  |  |
Net income | $ 82,151 | $ 78,409 | $ 76,425
Other comprehensive (loss) income, net of tax: |  |  |
Unrealized net holding (losses) arising during the year (pre-tax amounts of $(6,915), $(8,618) and $(3,159)) | (4,070) | (5,265) | (1,930)
Reclassification adjustment for net (gains) losses related to securities available for sale included in net income (pre-tax amounts of ($1,869), $644 and ($3,087)) | (1,153) | 393 | (1,886)
Reclassification adjustment for an impairment write-down of an equity security (pre-tax amounts of $1,312, $- and $-) | 811 | 0 | 0
Unrealized gains on derivatives (cash flow hedges) (pre-tax amounts of $609, $2,901 and $-) | 372 | 1,772 | 0
Amortization of unrealized net gains and losses related to the reclassification of available for sale securities to held to maturity (pre-tax amounts of $875, $1,094 and $1,311) | 540 | 668 | 801
Pension and other benefits: |  |  |
Amortization of prior service cost and actuarial gains (pre-tax amounts of $1,852, $2,370 and $2,239) | 1,112 | 1,421 | 1,371
Decrease (increase) in unrecognized actuarial loss (pre-tax amounts of $2,401, $3,154 and $(6,144)) | 1,831 | 1,909 | (3,747)
Total other comprehensive (loss) income | (557) | 898 | (5,391)
Comprehensive income | $ 81,594 | $ 79,307 | $ 71,034

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