Guarantor and Non-Guarantor Financial Statements, Cash Flow Statements (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities:
Net cash provided by operating activities1		$ 21.3	$ 7.4
Cash flows from investing activities3:
Capital expenditures		(25.9)	(11.3)
Proceeds from disposition of available for sale securities		20.0	84.0
Net cash used in investing activities	[1]	(5.9)	72.7
Cash flows from financing activities3:
Repayments of Long-term Capital Lease Obligations		0.0	(0.1)
Excess tax benefit upon vesting of non-vested shares and dividend payment on unvested shares expected to vest		0.0	1.0
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(2.7)	(2.5)
Repurchase of common stock		(6.3)	(28.2)
Cash dividends paid to stockholders		(8.2)	(7.1)
Receipts of cash dividends from distribution of third party trust		0.0
Intercompany loan		0.0	0.0
Net cash used in financing activities	[1]	(17.2)	(36.9)
Net (decrease) increase in cash and cash equivalents during the period		(1.8)	43.2
Cash and cash equivalents at beginning of period		72.5	177.7
Cash and cash equivalents at end of period		70.7	220.9
Parent
Cash flows from operating activities:
Net cash provided by operating activities1		17.2	37.8
Cash flows from investing activities3:
Capital expenditures		0.0	0.0
Proceeds from disposition of available for sale securities		0.0	0.0
Net cash used in investing activities		0.0	0.0
Cash flows from financing activities3:
Repayments of Long-term Capital Lease Obligations			0.0
Excess tax benefit upon vesting of non-vested shares and dividend payment on unvested shares expected to vest			0.0
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(2.7)	(2.5)
Repurchase of common stock		(6.3)	(28.2)
Cash dividends paid to stockholders		(8.2)	(7.1)
Receipts of cash dividends from distribution of third party trust		0.0
Intercompany loan		0.0	0.0
Net cash used in financing activities		(17.2)	(37.8)
Net (decrease) increase in cash and cash equivalents during the period		0.0	0.0
Cash and cash equivalents at beginning of period		0.0	0.0
Cash and cash equivalents at end of period		0.0	0.0
Guarantor Subsidiaries
Cash flows from operating activities:
Net cash provided by operating activities1		201.4	(32.7)
Cash flows from investing activities3:
Capital expenditures		(25.3)	(6.7)
Proceeds from disposition of available for sale securities		20.0	84.0
Net cash used in investing activities		(5.3)	77.3
Cash flows from financing activities3:
Repayments of Long-term Capital Lease Obligations			(0.1)
Excess tax benefit upon vesting of non-vested shares and dividend payment on unvested shares expected to vest			1.0
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		0.0	0.0
Repurchase of common stock		0.0	0.0
Cash dividends paid to stockholders		0.0	0.0
Receipts of cash dividends from distribution of third party trust		(200.0)
Intercompany loan		0.8	(1.9)
Net cash used in financing activities		(199.2)	(1.0)
Net (decrease) increase in cash and cash equivalents during the period		(3.1)	43.6
Cash and cash equivalents at beginning of period		72.2	175.3
Cash and cash equivalents at end of period		69.1	218.9
Non-Guarantor Subsidiaries
Cash flows from operating activities:
Net cash provided by operating activities1		2.7	2.3
Cash flows from investing activities3:
Capital expenditures		(0.6)	(4.6)
Proceeds from disposition of available for sale securities		0.0	0.0
Net cash used in investing activities		(0.6)	(4.6)
Cash flows from financing activities3:
Repayments of Long-term Capital Lease Obligations			0.0
Excess tax benefit upon vesting of non-vested shares and dividend payment on unvested shares expected to vest			0.0
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		0.0	0.0
Repurchase of common stock		0.0	0.0
Cash dividends paid to stockholders		0.0	0.0
Receipts of cash dividends from distribution of third party trust		0.0
Intercompany loan		(0.8)	1.9
Net cash used in financing activities		(0.8)	1.9
Net (decrease) increase in cash and cash equivalents during the period		1.3	(0.4)
Cash and cash equivalents at beginning of period		0.3	2.4
Cash and cash equivalents at end of period		1.6	2.0
Consolidating Adjustments
Cash flows from operating activities:
Net cash provided by operating activities1		(200.0)	0.0
Cash flows from investing activities3:
Capital expenditures		0.0	0.0
Proceeds from disposition of available for sale securities		0.0	0.0
Net cash used in investing activities		0.0	0.0
Cash flows from financing activities3:
Repayments of Long-term Capital Lease Obligations			0.0
Excess tax benefit upon vesting of non-vested shares and dividend payment on unvested shares expected to vest			0.0
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		0.0	0.0
Repurchase of common stock		0.0	0.0
Cash dividends paid to stockholders		0.0	0.0
Receipts of cash dividends from distribution of third party trust		200.0
Intercompany loan		0.0	0.0
Net cash used in financing activities		200.0	0.0
Net (decrease) increase in cash and cash equivalents during the period		0.0	0.0
Cash and cash equivalents at beginning of period		0.0	0.0
Cash and cash equivalents at end of period		$ 0.0	$ 0.0

[1] See Note 12 for the supplemental disclosure on non-cash transactions.