Condensed Guarantor and Non-Guarantor Financial Information, Cash Flow Statements (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net cash provided by (used in) operating activities	[1]			$ 84.0	$ 73.1
Cash flows from investing activities
Capital expenditures		$ (16.1)	$ (24.9)	(35.8)	(39.7)
Purchase of available for sale securities				(24.0)	(128.0)
Purchase of equity securities				(0.9)	0.0
Proceeds from disposition of available for sale securities				136.6	184.2
Intercompany loans receivable				0.0	0.0
Net cash provided by investing activities	[2]			75.9	16.5
Cash flows from financing activities
Repayment of capital lease				(0.3)	(0.1)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares				(6.9)	(4.5)
Repurchase of common stock				(18.9)	(64.4)
Cash dividends paid to Parent				0.0
Cash dividends and dividend equivalents paid				(19.3)	(17.9)
Intercompany loans payable				0.0	0.0
Net cash used in financing activities	[2]			(45.4)	(86.9)
Net increase in cash, cash equivalents, and restricted cash during the period				114.5	2.7
Cash, cash equivalents and restricted cash at beginning of period				64.3	67.7
Cash, cash equivalents and restricted cash at end of period		178.8	70.4	178.8	70.4
Consolidating Adjustments
Cash flows from operating activities:
Net cash provided by (used in) 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	0.0
Purchase of equity securities				0.0
Proceeds from disposition of available for sale securities				0.0	0.0
Intercompany loans receivable				41.7	(101.2)
Net cash provided by investing activities				41.7	(101.2)
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				(41.7)	101.2
Net cash used in financing activities				58.3	101.2
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	0.0	0.0
Parent
Cash flows from operating activities:
Net cash provided by (used in) operating activities				87.9	(12.3)
Cash flows from investing activities
Capital expenditures				0.0	0.0
Purchase of available for sale securities				0.0	0.0
Purchase of equity securities				0.0
Proceeds from disposition of available for sale securities				0.0	0.0
Intercompany loans receivable				(42.8)	99.1
Net cash provided by investing activities				(42.8)	99.1
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)	(4.5)
Repurchase of common stock				(18.9)	(64.4)
Cash dividends paid to Parent				0.0
Cash dividends and dividend equivalents paid				(19.3)	(17.9)
Intercompany loans payable				0.0	0.0
Net cash used in financing activities				(45.1)	(86.8)
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	0.0	0.0
Guarantor Subsidiaries
Cash flows from operating activities:
Net cash provided by (used in) operating activities				96.3	82.5
Cash flows from investing activities
Capital expenditures				(35.2)	(39.5)
Purchase of available for sale securities				(24.0)	(128.0)
Purchase of equity securities				(0.9)
Proceeds from disposition of available for sale securities				136.6	184.2
Intercompany loans receivable				0.0	(0.1)
Net cash provided by investing activities				76.5	16.6
Cash flows from financing activities
Repayment of capital lease				(0.3)	(0.1)
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				41.7	(101.2)
Net cash used in financing activities				(58.6)	(101.3)
Net increase in cash, cash equivalents, and restricted cash during the period				114.2	(2.2)
Cash, cash equivalents and restricted cash at beginning of period				61.3	65.1
Cash, cash equivalents and restricted cash at end of period		175.5	62.9	175.5	62.9
Non-Guarantor Subsidiaries
Cash flows from operating activities:
Net cash provided by (used in) operating activities				(0.2)	2.9
Cash flows from investing activities
Capital expenditures				(0.6)	(0.2)
Purchase of available for sale securities				0.0	0.0
Purchase of equity securities				0.0
Proceeds from disposition of available for sale securities				0.0	0.0
Intercompany loans receivable				1.1	2.2
Net cash provided by investing activities				0.5	2.0
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				0.3	4.9
Cash, cash equivalents and restricted cash at beginning of period				3.0	2.6
Cash, cash equivalents and restricted cash at end of period		$ 3.3	$ 7.5	$ 3.3	$ 7.5

[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.