Schedule II - Condensed Financial Information of the Registrant Cash Flow (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Statements of Cash Flows
Net income (loss)	$ 11,953	$ 18,597	$ 21,365	$ 12,670	$ 10,290	$ 11,981	$ (1,053)	$ (35,071)	$ 64,585	$ (13,853)	$ 59,354
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
(Earnings) loss from consolidated subsidiaries									(949)	(918)	(685)
Changes in assets and liabilities:
Other assets									348	(726)	(2,871)
Accounts payable and accrued liabilities									14,068	(12,423)	(577)
Net cash provided by operating activities									98,824	22,891	97,569
Proceeds from stock options exercised									257	278	297
Excess tax benefit from stock options exercised									(6)	1	3
Dividends paid									(42,265)	(41,976)	(39,302)
Acquisition of treasury stock											(23,467)
Net cash used for financing activities									(42,014)	(41,697)	(62,469)
Net increase in cash and cash equivalents									(27,442)	5,039	(13,422)
Cash and cash equivalents at beginning of year				$ 47,494				$ 42,455	47,494	42,455	55,877
Cash and cash equivalents at end of year	$ 20,052				$ 47,494				20,052	47,494	42,455
Registrant
Condensed Statements of Cash Flows
Net income (loss)									64,585	(13,853)	59,354
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
(Earnings) loss from consolidated subsidiaries									(65,991)	12,623	(60,618)
Dividends received from consolidated subsidiaries									39,156	39,440	59,186
Amortization of restricted stock expense									4,312	3,515	4,315
Changes in assets and liabilities:
Other assets									63	(33)	15
Accounts payable and accrued liabilities									(111)	5	217
Net cash provided by operating activities									42,014	41,697	62,469
Proceeds from stock options exercised									257	278	297
Excess tax benefit from stock options exercised									(6)	1	3
Dividends paid									(42,265)	(41,976)	(39,302)
Acquisition of treasury stock											(23,467)
Net cash used for financing activities									$ (42,014)	$ (41,697)	$ (62,469)