Schedule I - Financial Information of the Registrant (Parent Company) - Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of net income to cash (used) provided by operating activities:
Net income	$ 154,905	$ 78,615	$ 47,523
Add (deduct):
Depreciation	19,216	22,526	24,932
(Increase) decrease in receivables – net	(6,598)	(2,917)	5,280
(Increase) decrease in other assets – net	(5,380)	6,865	4,469
Increase (decrease) in payables and accrued liabilities – net	62,738	31,471	(12,002)
Income from and other adjustments for subsidiaries	(3,504)	(3,044)	(1,940)
Cash (used) provided by operating activities	275,806	166,359	84,177
Investing activities:
Cash (used) provided by investing activities	(231,370)	7,040	9,379
Financing activities:
Issuance of Common Stock	108,961	0	0
Dividends paid	(30,226)	(28,345)	(28,263)
Repurchases of Common Stock	(1,054)	(532)	(1,175)
Purchase of remaining interest of consolidated subsidiary	0	0	(1,101)
Cash provided (used) by financing activities	54,301	(37,762)	(47,758)
Increase in cash and cash equivalents	102,074	138,542	41,988
Cash and cash equivalents at beginning of year	330,609	192,067	150,079
Cash and cash equivalents at end of year	432,683	330,609	192,067
Supplemental information:
Income taxes paid, net	44,756	11,992	12,854
Interest paid	2,604	4,241	4,214
Parent company
Reconciliation of net income to cash (used) provided by operating activities:
Net income	154,905	78,615	47,523
Add (deduct):
Depreciation	4	8	4
(Increase) decrease in receivables – net	(1,998)	(253)	922
(Increase) decrease in other assets – net	(529)	1,659	853
Increase (decrease) in payables and accrued liabilities – net	2,978	2,698	(4,476)
Income from and other adjustments for subsidiaries	(170,816)	(43,240)	(45,793)
Cash (used) provided by operating activities	(15,456)	39,487	(967)
Investing activities:
Dividends from subsidiary	30,000	0	25,000
Collections on notes receivables	40,000	1,416	24,900
Increases in notes receivables	(80,000)	0	(5,193)
Investments in and contributions to subsidiaries	(85,470)	0	0
Cash (used) provided by investing activities	(95,470)	1,416	44,707
Financing activities:
Issuance of Common Stock	108,961	0	0
Dividends paid	(30,226)	(28,345)	(28,263)
Repurchases of Common Stock	(1,054)	(532)	(1,175)
Purchase of remaining interest of consolidated subsidiary	0	0	(1,101)
Cash provided (used) by financing activities	77,681	(28,877)	(30,539)
Increase in cash and cash equivalents	(33,245)	12,026	13,201
Cash and cash equivalents at beginning of year	36,849	24,823	11,622
Cash and cash equivalents at end of year	3,604	36,849	24,823
Supplemental information:
Income taxes paid, net	180	0	0
Interest paid	$ 2,490	$ 4,009	$ 3,849