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Equity Plans Restricted Stock and Deferred Restricted Stock Activity (Details) - USD ($) $ / shares in Units, $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested, Grant Date Fair Value | $ 2,420 | $ 1,913 | $ 2,775
Document Period End Date | Dec. 31, 2019 |  |
Cash received from employees toward purchases under the plan | $ 1,682 | $ 1,523 | $ 1,282
Employee stock purchase plan, shares | 30,255 | 25,907 | 27,743
Restricted Stock Awards, Performance-based, Issued, Intrinsic Value | 6,120 | 52,629 | 15,390
Restricted Stock Awards, Performance-based, Vested Balance | 7,676 |  |
Restricted Stock Awards, Performance-based, Outstanding Balance | 42,700 |  |
Incentive Plan [Member] |  |  |
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Number of shares reserved for issuance under the plan | 1,800,000 |  |
CTWS Plan [Member] |  |  |
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Number of shares reserved for issuance under the plan | 156,022 |  |
Employee Stock Purchase Plan [Member] |  |  |
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Expenses recorded under the plan | $ 294 | $ 265 | $ 229
Unrecognized compensation cost | $ 206 |  |
Purchase price of common stock to employees under the plan, percent | 85.00% |  |
Maximum amount of base salary employees can designate for share purchase under the plan | 10.00% |  |
Restricted Stock and Deferred Restricted Stock [Member] |  |  |
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Unrecognized compensation cost | $ 3,915 |  |
Period for recognition of compensation cost | 1 year 10 months 2 days |  |
Restricted Stock and Deferred Restricted Stock [Member] | Incentive Plan [Member] |  |  |
Restricted and Deferred Restricted Stock Awards Outstanding [Roll Forward] |  |  |
Outstanding as of January 1, 2016, units | 124,275 |  |
Issued, units | 76,018 |  |
Exercised, units | 25,529 |  |
Forfeited or expired | 0 |  |
Outstanding as of December 31, 2016, units | 174,764 | 124,275 |
Shares vested as of December 31, 2016, shares | 81,611 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Weighted Average Grant Date Fair Value [Roll Forward] [Roll Forward] |  |  |
Outstanding as of January 1, 2016, wtd avg grant date fair value | $ 38.80 |  |
Issued, wtd avg grant date fair value | 59.78 |  |
Exercised, wtd avg grant date fair value | 49.77 |  |
Forfeited or expired, wtd avg grant date fair value | 0 |  |
Outstanding as od December 31, 2016, wtd avg grant date fair value | 46.63 | $ 38.80 |
Shares vested as of December 31, 2016, wtd avg grant date fair value | $ 31.12 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |  |  |
Nonvested as of January 1, 2016, units | 55,098 |  |
Granted, units | 76,018 |  |
Vested, units | (37,963) |  |
Forfeited, units | 0 |  |
Nonvested as of December 31, 2016, units | 93,153 | 55,098 |
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Nonvested as of January 1, 2016, wtd avg grant date fair value | $ 54.42 |  |
Granted, wtd avg grant date fair value | 59.78 |  |
Vested, wtd avg grant date fair value | 59.27 |  |
Forfeited, wtd avg grant date fair value | 0 |  |
Nonvested as of December 31, 2016, wtd avg grant date fair value | $ 39.57 | $ 54.42 |
Restricted Stock and Deferred Restricted Stock [Member] | CTWS Plan [Member] |  |  |
Restricted and Deferred Restricted Stock Awards Outstanding [Roll Forward] |  |  |
Issued, units | 105,233 |  |
Exercised, units | 23 |  |
Forfeited or expired | 2,279 |  |
Outstanding as of December 31, 2016, units | 102,931 |  |
Deferred Restricted Stock Awards [Member] |  |  |
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Cumulative dividend equivalent rights converted to deferred restricted stock awards | 81,231 | 79,478 | 77,034
Dividend Equivalent Rights [Member] |  |  |
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Liability for dividend equivalent rights | $ 93 | $ 97 | $ 139
Common Stock [Member] | Employee Stock Purchase Plan [Member] |  |  |
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |
Number of shares reserved for issuance under the plan | 400,000 |  |

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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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