Condensed Guarantor and Non-Guarantor Financial Information, Cash Flow Statements (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net cash provided by operating activities	[1]	$ 26.1	$ 4.1
Cash flows from investing activities
Capital expenditures		(19.7)	(14.8)
Purchase of available for sale securities		0.0	(74.7)
Proceeds from disposition of available for sale securities		100.3	110.9
Intercompany loans receivable		0.0	0.0
Net cash provided by investing activities	[2]	80.6	21.4
Cash flows from financing activities
Repayment of capital lease		(0.2)	(0.2)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(6.9)	(4.4)
Repurchase of common stock		(5.7)	(32.6)
Cash dividends paid to Parent		0.0
Cash dividends and dividend equivalents paid		(10.0)	(9.3)
Intercompany loans payable		0.0	0.0
Net cash (used in) financing activities	[2]	(22.8)	(46.5)
Net increase in cash, cash equivalents, and restricted cash during the period		83.9	(21.0)
Cash, cash equivalents and restricted cash at beginning of period		64.3	67.7
Cash, cash equivalents and restricted cash at end of period		148.2	46.7
Consolidating Adjustments
Cash flows from operating activities:
Net cash provided by operating activities		(100.0)	0.0
Cash flows from investing activities
Capital expenditures		0.0	0.0
Purchase of available for sale securities			0.0
Proceeds from disposition of available for sale securities		0.0	0.0
Intercompany loans receivable		77.0	(47.3)
Net cash provided by investing activities		77.0	(47.3)
Cash flows from financing activities
Repayment of capital lease		0.0	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 Parent		100.0
Cash dividends and dividend equivalents paid		0.0	0.0
Intercompany loans payable		(77.0)	47.3
Net cash (used in) financing activities		23.0	47.3
Net increase in cash, cash equivalents, and restricted cash during the period		0.0	0.0
Cash, cash equivalents and restricted cash at beginning of period		0.0	0.0
Cash, cash equivalents and restricted cash at end of period		0.0	0.0
Parent
Cash flows from operating activities:
Net cash provided by operating activities		99.7	(0.3)
Cash flows from investing activities
Capital expenditures		0.0	0.0
Purchase of available for sale securities			0.0
Proceeds from disposition of available for sale securities		0.0	0.0
Intercompany loans receivable		(77.1)	46.6
Net cash provided by investing activities		(77.1)	46.6
Cash flows from financing activities
Repayment of capital lease		0.0	0.0
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(6.9)	(4.4)
Repurchase of common stock		(5.7)	(32.6)
Cash dividends paid to Parent		0.0
Cash dividends and dividend equivalents paid		(10.0)	(9.3)
Intercompany loans payable		0.0	0.0
Net cash (used in) financing activities		(22.6)	(46.3)
Net increase in cash, cash equivalents, and restricted cash during the period		0.0	0.0
Cash, cash equivalents and restricted cash at beginning of period		0.0	0.0
Cash, cash equivalents and restricted cash at end of period		0.0	0.0
Guarantor Subsidiaries
Cash flows from operating activities:
Net cash provided by operating activities		25.6	2.6
Cash flows from investing activities
Capital expenditures		(19.4)	(14.7)
Purchase of available for sale securities			(74.7)
Proceeds from disposition of available for sale securities		100.3	110.9
Intercompany loans receivable		0.0	0.0
Net cash provided by investing activities		80.9	21.5
Cash flows from financing activities
Repayment of capital lease		(0.2)	(0.2)
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 Parent		(100.0)
Cash dividends and dividend equivalents paid		0.0	0.0
Intercompany loans payable		77.0	(47.3)
Net cash (used in) financing activities		(23.2)	(47.5)
Net increase in cash, cash equivalents, and restricted cash during the period		83.3	(23.4)
Cash, cash equivalents and restricted cash at beginning of period		61.3	65.1
Cash, cash equivalents and restricted cash at end of period		144.6	41.7
Non-Guarantor Subsidiaries
Cash flows from operating activities:
Net cash provided by operating activities		0.8	1.8
Cash flows from investing activities
Capital expenditures		(0.3)	(0.1)
Purchase of available for sale securities			0.0
Proceeds from disposition of available for sale securities		0.0	0.0
Intercompany loans receivable		0.1	0.7
Net cash provided by investing activities		(0.2)	0.6
Cash flows from financing activities
Repayment of capital lease		0.0	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 Parent		0.0
Cash dividends and dividend equivalents paid		0.0	0.0
Intercompany loans payable		0.0	0.0
Net cash (used in) financing activities		0.0	0.0
Net increase in cash, cash equivalents, and restricted cash during the period		0.6	2.4
Cash, cash equivalents and restricted cash at beginning of period		3.0	2.6
Cash, cash equivalents and restricted cash at end of period		$ 3.6	$ 5.0

[1] See Note 8 for adjustments made to arrive at our Consolidated Balance Sheet as of January 1, 2018 upon adopting ASC 606 (as defined in Note 1).

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