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Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Operating Activities |  |  |  |  |  |  |  |  |  |  |
Net income | $ 14,956 | $ 36,479 | $ 33,687 | $ 31,255 | $ 31,041 | $ 30,957 | $ 30,451 | $ 28,682 | $ 116,377 | $ 121,131 | $ 116,127
Adjustments to reconcile net income to net cash provided by operating activities: |  |  |  |  |  |  |  |  |  |  |
Amortization of purchase accounting adjustments |  |  |  |  |  |  |  |  | (5,131) | (2,252) | 1,264
Gain on sale of investments |  |  |  |  |  |  |  |  | 660 | 1,463 | (19)
Stock-based compensation, net of tax benefits |  |  |  |  |  |  |  |  | 2,952 | 1,844 | 1,695
Net cash provided by operating activities |  |  |  |  |  |  |  |  | 254,741 | 193,087 | 176,771
Investing Activities |  |  |  |  |  |  |  |  |  |  |
Sales of available-for-sale securities |  |  |  |  |  |  |  |  | 247,748 | 62,817 | 136,777
Net cash used in by investing activities |  |  |  |  |  |  |  |  | 23,655 | (421,313) | (681,314)
Financing Activities |  |  |  |  |  |  |  |  |  |  |
Cash dividends paid |  |  |  |  |  |  |  |  | (111,720) | (84,040) | (79,456)
Tax withholding payments for stock-based compensation |  |  |  |  |  |  |  |  | (1,531) | (600) | (489)
Net cash used in financing activities |  |  |  |  |  |  |  |  | (230,933) | 187,514 | 255,387
Net (decrease) increase in cash and cash equivalents |  |  |  |  |  |  |  |  | 47,463 | (40,712) | (249,156)
Cash and cash equivalents at beginning of period |  |  |  | 152,541 |  |  |  | 193,253 | 152,541 | 193,253 | 442,409
Cash and cash equivalents at end of period | 200,004 |  |  |  | 152,541 |  |  |  | 200,004 | 152,541 | 193,253
Parent Company |  |  |  |  |  |  |  |  |  |  |
Operating Activities |  |  |  |  |  |  |  |  |  |  |
Net income |  |  |  |  |  |  |  |  | 116,377 | 121,131 | 116,127
Adjustments to reconcile net income to net cash provided by operating activities: |  |  |  |  |  |  |  |  |  |  |
Subsidiary income in excess of dividends distributed |  |  |  |  |  |  |  |  | (8,156) | (19,548) | (13,782)
Amortization of purchase accounting adjustments |  |  |  |  |  |  |  |  | 143 | 143 | 143
Gain on sale of investments |  |  |  |  |  |  |  |  | (3) | 0 | 0
Stock-based compensation, net of tax benefits |  |  |  |  |  |  |  |  | 1,460 | 804 | 695
Net change in other assets and other liabilities |  |  |  |  |  |  |  |  | 5,051 | (297) | 118
Net cash provided by operating activities |  |  |  |  |  |  |  |  | 114,872 | 102,233 | 103,301
Investing Activities |  |  |  |  |  |  |  |  |  |  |
Sales of available-for-sale securities |  |  |  |  |  |  |  |  | 27 | 0 | 0
Net (increase) decrease of premises and equipment |  |  |  |  |  |  |  |  | (79) | 771 | (1,405)
Proceeds from sale of non-marketable equity securities |  |  |  |  |  |  |  |  | 114 | 55 | 22
Equity contribution to subsidiaries |  |  |  |  |  |  |  |  | (17,565) | (3,475) | (28,457)
Net cash used in by investing activities |  |  |  |  |  |  |  |  | (17,503) | (2,649) | (29,840)
Financing Activities |  |  |  |  |  |  |  |  |  |  |
Cash dividends paid |  |  |  |  |  |  |  |  | (111,720) | (84,040) | (79,456)
Tax withholding payments for stock-based compensation |  |  |  |  |  |  |  |  | (1,531) | (600) | (489)
Net cash used in financing activities |  |  |  |  |  |  |  |  | (113,251) | (84,640) | (79,945)
Net (decrease) increase in cash and cash equivalents |  |  |  |  |  |  |  |  | (15,882) | 14,944 | (6,484)
Cash and cash equivalents at beginning of period |  |  |  | $ 63,606 |  |  |  | $ 48,662 | 63,606 | 48,662 | 55,146
Cash and cash equivalents at end of period | $ 47,724 |  |  |  | $ 63,606 |  |  |  | $ 47,724 | $ 63,606 | $ 48,662

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- Definition Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6676-107765 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3044-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.1) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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