Condensed Consolidating Financial Information - Cash Flows (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Condensed Consolidating Statements Of Cash Flows
Net cash provided by (used for) operating activities	$ 273,085	$ 77,357
Cash flows from investing activities:
Purchases of investments	(4,572)	(676)
Sales and maturities of investments	11,919	2,602
Cash paid for acquisitions of businesses, net of cash acquired	(2,929)
Capital expenditures	(274,479)	(209,471)
Proceeds from sales of assets and insurance claims	11,857	77,272
Net cash (used for) provided by investing activities	(258,204)	(130,273)
Cash flows from financing activities:
Increase (decrease) in cash overdrafts		(344)
Debt issuance costs	(49)	(12,990)
Proceeds from (payments for) issuance of common shares		302,014
Reduction of long-term debt	(361,966)	(460,837)
Proceeds from (payments for) commercial paper, net		(40,000)
Proceeds from revolving credit facilities	790,000	625,000
Reduction in revolving credit facilities	(480,000)	(1,135,000)
Dividends to common and preferred shareholders	(33,705)	(36,200)
Proceeds from (payments for) short-term borrowings	229	62
Proceeds from issuance of preferred stock, net of issuance costs		278,573
Proceeds from issuance of long-term debt		800,000
Distributions to noncontrolling interest	(814)	(4,676)
Other changes	(2,337)	(3,688)
Net cash (used for) provided by financing activities	(88,642)	311,914
Effect of exchange rate changes on cash and cash equivalents	(1,968)	(3,637)
Net increase (decrease) in cash, cash equivalents and restricted cash	(75,729)	255,361
Cash and cash equivalents and restricted cash, beginning of period	451,080	342,029
Cash and cash equivalents and restricted cash, end of period	375,351	597,390
Consolidating Adjustments
Condensed Consolidating Statements Of Cash Flows
Net cash provided by (used for) operating activities	(58,996)	(28,149)
Cash flows from investing activities:
Cash paid for investments in consolidated affiliates	8,500	786,500
Net cash (used for) provided by investing activities	8,500	786,500
Cash flows from financing activities:
Dividends to common and preferred shareholders	3,696	6,149
Proceeds from parent contributions	(8,500)	(786,500)
Distribution from subsidiary to parent	55,300	22,000
Net cash (used for) provided by financing activities	50,496	(758,351)
Parent Company | Reportable Legal Entities
Condensed Consolidating Statements Of Cash Flows
Net cash provided by (used for) operating activities	59,249	56,041
Cash flows from investing activities:
Cash paid for investments in consolidated affiliates		(587,500)
Net cash (used for) provided by investing activities		(587,500)
Cash flows from financing activities:
Proceeds from (payments for) issuance of common shares	6	302,014
Proceeds from issuance of intercompany debt	4,700	20,000
Dividends to common and preferred shareholders	(36,926)	(42,349)
Proceeds from issuance of preferred stock, net of issuance costs		278,573
Paydown of intercompany debt	(25,500)	(21,000)
Other changes	(1,680)	(3,688)
Net cash (used for) provided by financing activities	(59,400)	533,550
Net increase (decrease) in cash, cash equivalents and restricted cash	(151)	2,091
Cash and cash equivalents and restricted cash, beginning of period	474	1,091
Cash and cash equivalents and restricted cash, end of period	323	3,182
Guarantor Subsidiaries | Reportable Legal Entities
Condensed Consolidating Statements Of Cash Flows
Net cash provided by (used for) operating activities	(91,938)	(102,233)
Cash flows from investing activities:
Change in intercompany balances	142,645	127,059
Net cash (used for) provided by investing activities	142,645	127,059
Cash flows from financing activities:
Debt issuance costs	(49)	(12,990)
Reduction of long-term debt	(361,966)	(460,837)
Proceeds from (payments for) commercial paper, net		(40,000)
Proceeds from revolving credit facilities	790,000	625,000
Reduction in revolving credit facilities	(480,000)	(1,135,000)
Proceeds from issuance of long-term debt		800,000
Paydown of intercompany debt	(7,194)
Proceeds from parent contributions	8,500	199,000
Net cash (used for) provided by financing activities	(50,709)	(24,827)
Net increase (decrease) in cash, cash equivalents and restricted cash	(2)	(1)
Cash and cash equivalents and restricted cash, beginning of period	42	44
Cash and cash equivalents and restricted cash, end of period	40	43
Other Subsidiaries (Non-Guarantors) | Reportable Legal Entities
Condensed Consolidating Statements Of Cash Flows
Net cash provided by (used for) operating activities	364,770	151,698
Cash flows from investing activities:
Purchases of investments	(4,572)	(676)
Sales and maturities of investments	11,919	2,602
Cash paid for acquisitions of businesses, net of cash acquired	(2,929)
Cash paid for investments in consolidated affiliates	(8,500)	(199,000)
Capital expenditures	(274,479)	(209,471)
Proceeds from sales of assets and insurance claims	11,857	77,272
Change in intercompany balances	(142,645)	(127,059)
Net cash (used for) provided by investing activities	(409,349)	(456,332)
Cash flows from financing activities:
Increase (decrease) in cash overdrafts		(344)
Proceeds from (payments for) issuance of common shares	(6)
Proceeds from issuance of intercompany debt	(4,700)	(20,000)
Dividends to common and preferred shareholders	(475)
Proceeds from (payments for) short-term borrowings	229	62
Paydown of intercompany debt	32,694	21,000
Distributions to noncontrolling interest	(814)	(4,676)
Proceeds from parent contributions		587,500
Distribution from subsidiary to parent	(55,300)	(22,000)
Other changes	(657)
Net cash (used for) provided by financing activities	(29,029)	561,542
Effect of exchange rate changes on cash and cash equivalents	(1,968)	(3,637)
Net increase (decrease) in cash, cash equivalents and restricted cash	(75,576)	253,271
Cash and cash equivalents and restricted cash, beginning of period	450,564	340,894
Cash and cash equivalents and restricted cash, end of period	$ 374,988	$ 594,165