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Stock-Based Compensation (Details) - USD ($) |  |  | 6 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 02, 2018 | Mar. 03, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2017 | Feb. 28, 2018 | Feb. 28, 2017 | Mar. 31, 2015 | Jan. 01, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Vesting period |  |  | 1 year |  |  |  |  |  |
Unrecognized expense related to stock awards |  |  | $ 5,400,000 |  | $ 3,800,000 |  |  |  |
Restricted Stock, Shares |  |  |  |  |  |  |  |  |
Expired (in shares) |  |  | 0 |  |  |  |  |  |
Restricted Stock, Weighted- Average Grant Date Fair Value |  |  |  |  |  |  |  |  |
Expired (in dollars per share) |  |  | $ 0.00 |  |  |  |  |  |
Stock Options, Shares |  |  |  |  |  |  |  |  |
Outstanding at beginning of period (in shares) |  |  | 193,441 |  |  |  |  |  |
Granted (in shares) |  |  | 0 |  |  |  |  |  |
Exercised (in shares) |  |  | (107,941) |  |  |  |  |  |
Forfeited (in shares) |  |  | 0 |  |  |  |  |  |
Expired (in shares) |  |  | 0 |  |  |  |  |  |
Outstanding at end of period (in shares) |  |  | 85,500 |  | 193,441 |  |  |  |
Stock Options, Weighted- Average Exercise Price |  |  |  |  |  |  |  |  |
Outstanding at beginning of period (in dollars per share) |  |  | $ 9.98 |  |  |  |  |  |
Granted (in dollars per share) |  |  | 0.00 |  |  |  |  |  |
Exercised (in dollars per share) |  |  | 8.56 |  |  |  |  |  |
Forfeited (in dollars per share) |  |  | 0.00 |  |  |  |  |  |
Expired (in dollars per share) |  |  | 0.00 |  |  |  |  |  |
Outstanding at end of period (in dollars per share) |  |  | 11.77 |  | $ 9.98 |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] |  |  |  |  |  |  |  |  |
Weighted-average grant date fair value of options granted (in dollars per share) |  |  | $ 0.00 | $ 0.00 |  |  |  |  |
Total fair value of options that vested |  |  | $ 0 | $ 0 |  |  |  |  |
Total intrinsic value of options exercised |  |  | $ 2,968,000 | $ 1,699,000 |  |  |  |  |
Executive Vice President and Chief Financial Officer | Common Stock | Achieved performance target for 2015 and 2016 |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Value of stock awarded |  |  |  |  |  |  |  |  | $ 100,000
Number of shares available for grant |  |  |  |  |  | 275,000 | 100,000 |  |
Restricted Stock, Shares |  |  |  |  |  |  |  |  |
Granted (in shares) | 7,670 | 2,754 |  |  |  |  |  |  |
Restricted Stock, Weighted- Average Grant Date Fair Value |  |  |  |  |  |  |  |  |
Granted (in dollars per share) | $ 35.85 | $ 36.30 |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] |  |  |  |  |  |  |  |  |
Weighted-average grant date fair value (in dollars per share) | $ 35.85 | $ 36.30 |  |  |  |  |  |  |
Executive Vice President and Chief Financial Officer | Common Stock | Achieved performance target for 2015, 2016 and 2017 |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Value of stock awarded |  |  |  |  |  |  |  |  | $ 275,000
Chairman, President, and Chief Executive Officer | Common Stock | Achieves a specific performance target by the end of 2019 and she remains an employee |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Shares received if achieves specified improvement in total shareholders return (in shares) |  |  |  |  |  |  |  | 53,859 |
Chairman, President, and Chief Executive Officer | Common Stock | Achieves a specific performance target by the end of 2017 and she remains an employee |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Shares received if achieves specified improvement in total shareholders return (in shares) |  |  |  |  |  |  |  | 17,953 |
Restricted Shares and Performance Based Shares |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Period of time stock expense is expected to be recognized |  |  | 1 year 9 months 15 days |  | 1 year 6 months 11 days |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] |  |  |  |  |  |  |  |  |
Expected quarterly dividends per share (in dollars per share) |  |  | $ 0.2650 | $ 0.2425 |  |  |  |  |
Risk-free interest rate |  |  | 2.38% | 1.50% |  |  |  |  |
Restricted Stock |  |  |  |  |  |  |  |  |
Restricted Stock, Shares |  |  |  |  |  |  |  |  |
Outstanding at beginning of period (in shares) |  |  | 189,045 |  |  |  |  |  |
Granted (in shares) |  |  | 221,062 |  |  |  |  |  |
Exercised (in shares) |  |  | (231,735) |  |  |  |  |  |
Forfeited (in shares) |  |  | (3,562) |  |  |  |  |  |
Expired (in shares) |  |  | 0 |  |  |  |  |  |
Outstanding at end of period (in shares) |  |  | 174,810 |  | 189,045 |  |  |  |
Restricted Stock, Weighted- Average Grant Date Fair Value |  |  |  |  |  |  |  |  |
Outstanding at beginning of period (in dollars per share) |  |  | $ 31.11 |  |  |  |  |  |
Granted (in dollars per share) |  |  | 29.65 | $ 23.06 |  |  |  |  |
Exercised (in dollars per share) |  |  | 28.37 |  |  |  |  |  |
Forfeited (in dollars per share) |  |  | 30.58 |  |  |  |  |  |
Expired (in dollars per share) |  |  | 0.00 |  |  |  |  |  |
Outstanding at end of period (in dollars per share) |  |  | $ 32.90 |  | $ 31.11 |  |  |  |
Stock Options, Shares |  |  |  |  |  |  |  |  |
Expired (in shares) |  |  | 0 |  |  |  |  |  |
Stock Options, Weighted- Average Exercise Price |  |  |  |  |  |  |  |  |
Expired (in dollars per share) |  |  | $ 0.00 |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] |  |  |  |  |  |  |  |  |
Weighted-average grant date fair value (in dollars per share) |  |  | $ 29.65 | $ 23.06 |  |  |  |  |
Total fair value of restricted shares that vested |  |  | $ 8,328,000 | $ 5,489,000 |  |  |  |  |
Performance Shares | Executive |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Shares granted (in shares) |  |  | 97,697 |  |  |  |  |  |
Weighted percentage assigned to achieving market targets |  |  | 60.00% |  |  |  |  |  |
Weighted percentage assigned to achieving performance targets |  |  | 40.00% |  |  |  |  |  |
Maximum number of shares awarded in year 1 (in shares) |  |  | 138,081 |  |  |  |  |  |
Maximum number of shares awarded in year 2 (in shares) |  |  | 135,818 |  |  |  |  |  |
Maximum number of shares awarded in year 3 (in shares) |  |  | 152,750 |  |  |  |  |  |
Performance period |  |  | 3 years |  |  |  |  |  |
Market-Based Shares |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] |  |  |  |  |  |  |  |  |
Risk-free interest rate |  |  | 2.36% | 1.54% |  |  |  |  |
Dividend yield |  |  | 2.96% | 2.67% |  |  |  |  |
Expected volatility |  |  | 19.12% | 20.80% |  |  |  |  |
Stock options |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Aggregate intrinsic value of stock options outstanding |  |  | $ 2,300,000 |  |  |  |  |  |
Weighted-average remaining contract life |  |  | 1 year 6 months |  |  |  |  |  |
Number of outstanding stock options with an exercise price greater than the closing price (in shares) |  |  | 0 |  |  |  |  |  |
Performance Equity Plan |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Vesting period |  |  | 3 years |  |  |  |  |  |
Vesting rate |  |  | 100.00% |  |  |  |  |  |

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- Definition Unrecognized cost of unvested share-based compensation awards. + 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 (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (a)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The number of grants made 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=109197908&loc=d3e5070-113901 + Details
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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=109197908&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units. + 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)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. + 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 (f)(2)(iii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + 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 (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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