Condensed Consolidating Financial Information (Statements of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	$ 40,714	$ 27,896
Cash flows from investing activities:
Purchase of equity securities	(998)	0
Sale of equity securities	358	0
Maturities of equity securities	302	0
Purchase of debt securities	(3,366)	(14,974)
Purchase of long-term investments	0	(22,400)
Investments in real estate ventures	(533)	(1,436)
Distributions from investments in real estate ventures	219	0
Increase in cash surrender value of life insurance policies	(36)	(49)
(Increase) decrease in restricted assets	(4)	2,104
Issuance of notes receivable	0	(1,500)
Investments in subsidiaries	0	0
Proceeds from sale of fixed assets	0	2
Capital expenditures	(3,987)	(4,588)
Repayments of notes receivable	32	0
Pay downs of investment securities	446	864
Investments in real estate, net	(355)	(70)
Net cash provided by (used in) investing activities	1,887	(21,417)
Cash flows from financing activities:
Proceeds from issuance of debt	0	850,000
Deferred financing costs	0	(19,200)
Repayments of debt	(490)	(835,697)
Borrowings under revolver	55,170	39,956
Repayments on revolver	(61,728)	(68,305)
Capital contributions received	0	0
Intercompany dividends paid	0	0
Dividends and distributions on common stock	(57,187)	(52,358)
Proceeds from issuance of Vector common stock	0	43,230
Net cash used in financing activities	(64,235)	(42,374)
Net decrease in cash, cash equivalents and restricted cash	(21,634)	(35,895)
Cash, cash equivalents and restricted cash, beginning of period	310,937	398,608
Cash, cash equivalents and restricted cash, end of period	289,303	362,713
Sale of debt securities	1,999	13,456
Maturities of debt securities	7,810	7,174
Consolidating Adjustments
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	(43,154)	(47,657)
Cash flows from investing activities:
Purchase of equity securities	0
Sale of equity securities	0
Maturities of equity securities	0
Purchase of debt securities	0	0
Purchase of long-term investments		0
Investments in real estate ventures	0	0
Distributions from investments in real estate ventures	0
Increase in cash surrender value of life insurance policies	0	0
(Increase) decrease in restricted assets	0	0
Issuance of notes receivable		0
Investments in subsidiaries	605	535
Proceeds from sale of fixed assets		0
Capital expenditures	0	0
Repayments of notes receivable	(20,000)
Pay downs of investment securities	0	0
Investments in real estate, net	0	0
Net cash provided by (used in) investing activities	(19,395)	535
Cash flows from financing activities:
Proceeds from issuance of debt		0
Deferred financing costs		0
Repayments of debt	20,000	0
Borrowings under revolver	0	0
Repayments on revolver	0	0
Capital contributions received	(605)	(535)
Intercompany dividends paid	43,154	47,657
Dividends and distributions on common stock	0	0
Proceeds from issuance of Vector common stock		0
Net cash used in financing activities	62,549	47,122
Net decrease in cash, cash equivalents and restricted cash	0	0
Cash, cash equivalents and restricted cash, beginning of period	0	0
Cash, cash equivalents and restricted cash, end of period	0	0
Sale of debt securities	0	0
Maturities of debt securities	0	0
Parent/Issuer | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	18,670	(28,282)
Cash flows from investing activities:
Purchase of equity securities	(998)
Sale of equity securities	358
Maturities of equity securities	302
Purchase of debt securities	(3,366)	(14,974)
Purchase of long-term investments		(22,400)
Investments in real estate ventures	0	0
Distributions from investments in real estate ventures	0
Increase in cash surrender value of life insurance policies	11	0
(Increase) decrease in restricted assets	(4)	(3)
Issuance of notes receivable		0
Investments in subsidiaries	(605)	(535)
Proceeds from sale of fixed assets		0
Capital expenditures	(5)	(6)
Repayments of notes receivable	20,000
Pay downs of investment securities	446	864
Investments in real estate, net	0	0
Net cash provided by (used in) investing activities	25,948	(16,424)
Cash flows from financing activities:
Proceeds from issuance of debt		850,000
Deferred financing costs		(19,200)
Repayments of debt	0	(835,000)
Borrowings under revolver	0	0
Repayments on revolver	0	0
Capital contributions received	0	0
Intercompany dividends paid	0	0
Dividends and distributions on common stock	(57,187)	(52,358)
Proceeds from issuance of Vector common stock		43,230
Net cash used in financing activities	(57,187)	(13,328)
Net decrease in cash, cash equivalents and restricted cash	(12,569)	(58,034)
Cash, cash equivalents and restricted cash, beginning of period	194,719	279,815
Cash, cash equivalents and restricted cash, end of period	182,150	221,781
Sale of debt securities	1,999	13,456
Maturities of debt securities	7,810	7,174
Subsidiary Guarantors | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	74,867	95,873
Cash flows from investing activities:
Purchase of equity securities	0
Sale of equity securities	0
Maturities of equity securities	0
Purchase of debt securities	0	0
Purchase of long-term investments		0
Investments in real estate ventures	0	0
Distributions from investments in real estate ventures	0
Increase in cash surrender value of life insurance policies	(47)	(49)
(Increase) decrease in restricted assets	0	1,355
Issuance of notes receivable		0
Investments in subsidiaries	0	0
Proceeds from sale of fixed assets		2
Capital expenditures	(911)	(1,096)
Repayments of notes receivable	0
Pay downs of investment securities	0	0
Investments in real estate, net	0	0
Net cash provided by (used in) investing activities	(958)	212
Cash flows from financing activities:
Proceeds from issuance of debt		0
Deferred financing costs		0
Repayments of debt	(20,422)	(654)
Borrowings under revolver	55,170	39,956
Repayments on revolver	(61,728)	(68,305)
Capital contributions received	350	100
Intercompany dividends paid	(40,119)	(45,646)
Dividends and distributions on common stock	0	0
Proceeds from issuance of Vector common stock		0
Net cash used in financing activities	(66,749)	(74,549)
Net decrease in cash, cash equivalents and restricted cash	7,160	21,536
Cash, cash equivalents and restricted cash, beginning of period	20,175	19,684
Cash, cash equivalents and restricted cash, end of period	27,335	41,220
Sale of debt securities	0	0
Maturities of debt securities	0	0
Subsidiary Non-Guarantors | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	(9,669)	7,962
Cash flows from investing activities:
Purchase of equity securities	0
Sale of equity securities	0
Maturities of equity securities	0
Purchase of debt securities	0	0
Purchase of long-term investments		0
Investments in real estate ventures	(533)	(1,436)
Distributions from investments in real estate ventures	219
Increase in cash surrender value of life insurance policies	0	0
(Increase) decrease in restricted assets	0	752
Issuance of notes receivable		(1,500)
Investments in subsidiaries	0	0
Proceeds from sale of fixed assets		0
Capital expenditures	(3,071)	(3,486)
Repayments of notes receivable	32
Pay downs of investment securities	0	0
Investments in real estate, net	(355)	(70)
Net cash provided by (used in) investing activities	(3,708)	(5,740)
Cash flows from financing activities:
Proceeds from issuance of debt		0
Deferred financing costs		0
Repayments of debt	(68)	(43)
Borrowings under revolver	0	0
Repayments on revolver	0	0
Capital contributions received	255	435
Intercompany dividends paid	(3,035)	(2,011)
Dividends and distributions on common stock	0	0
Proceeds from issuance of Vector common stock		0
Net cash used in financing activities	(2,848)	(1,619)
Net decrease in cash, cash equivalents and restricted cash	(16,225)	603
Cash, cash equivalents and restricted cash, beginning of period	96,043	99,109
Cash, cash equivalents and restricted cash, end of period	79,818	99,712
Sale of debt securities	0	0
Maturities of debt securities	$ 0	$ 0