SCHEDULE I - CONDENSED FINANCIAL INFORMATION OF PARENT 3 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed financial statements
Net Cash Provided by (Used in) Operating Activities	$ 116,864	$ 136,774	$ 144,552
Cash Flows From Investing Activities:
Net Cash Provided by (Used in) Investing Activities	(153,195)	(128,042)	(80,031)
Cash Flows From Financing Activities:
Proceeds from stock option exercises	519	546	909
Dividends paid	(42,702)	(38,937)	(36,417)
Cash and cash equivalents, beginning of period	7,141	214	436
Cash and cash equivalents, end of year	1,334	7,141	214
Net Cash Provided by (Used in) Financing Activities	30,524	(1,805)	(64,743)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect	(5,807)	6,927	(222)
Parent Company
Condensed financial statements
Net Cash Provided by (Used in) Operating Activities	40,459	79,877	36,024
Cash Flows From Investing Activities:
Loans (made to)/repaid from, wholly-owned subsidiaries	(107,500)	(30,500)	30,500
Investment Company, Net Assets, Period Increase (Decrease)	0	(47,500)	0
Net Cash Provided by (Used in) Investing Activities	(107,500)	(78,000)	30,500
Cash Flows From Financing Activities:
Proceeds from stock option exercises	519	546	909
Net change in notes payable to banks	(109,500)	(36,500)	31,000
Dividends paid	(42,702)	(38,937)	(36,417)
Cash and cash equivalents, beginning of period	34	48	32
Cash and cash equivalents, end of year	310	34	48
Net Cash Provided by (Used in) Financing Activities	67,317	(1,891)	(66,508)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect	$ 276	$ (14)	$ 16