Guarantor and Non-Guarantor Financial Statements, Cash Flow Statements (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operating activities:
Net cash provided by (used in) operating activities			$ 108.9	$ 103.7
Cash flows from investing activities:
Capital expenditures	$ (15.5)	$ (9.5)	(38.4)	(39.6)
Purchase of available for sale securities			(0.5)	(53.4)
Proceeds from disposition of available for sale securities			84.0	82.2
Change in restricted cash			0.0	(0.7)
Net cash provided by (used in) investing activities			45.1	(11.5)
Cash flows from financing activities:
Repurchase of Senior Notes2			(6.1)	0.0
Settlement of Convertible Notes2			(175.0)	0.0
Proceeds from cash-settled call options related to settlement of Convertible Notes2			94.9	0.0
Payment for conversion premium related to settlement of Convertible Notes2			(94.9)	0.0
Excess tax benefit upon vesting of non-vested shares and dividend payment on unvested shares expected to vest			1.1	0.8
Cancellation of shares to cover employees’ tax withholdings upon vesting of non-vested shares			(3.0)	(2.4)
Repurchase of common stock			(45.1)	(28.7)
Cash dividend paid to stockholders			(21.0)	(19.1)
Intercompany loan			0.0	0.0
Net cash used in financing activities			(249.1)	(49.4)
Net (decrease) increase in cash and cash equivalents during the period			(95.1)	42.8
Cash and cash equivalents at beginning of period			177.7	169.5
Cash and cash equivalents at end of period	82.6	212.3	82.6	212.3
Parent
Cash flows from operating activities:
Net cash provided by (used in) operating activities			250.2	13.9
Cash flows from investing activities:
Capital expenditures			0.0	0.0
Purchase of available for sale securities			0.0	0.0
Proceeds from disposition of available for sale securities			0.0	0.0
Change in restricted cash				0.0
Net cash provided by (used in) investing activities			0.0	0.0
Cash flows from financing activities:
Repurchase of Senior Notes2			(6.1)
Settlement of Convertible Notes2			(175.0)
Proceeds from cash-settled call options related to settlement of Convertible Notes2			94.9
Payment for conversion premium related to settlement of Convertible Notes2			(94.9)
Excess tax benefit upon vesting of non-vested shares and dividend payment on unvested shares expected to vest			0.0	0.0
Cancellation of shares to cover employees’ tax withholdings upon vesting of non-vested shares			(3.0)	(2.4)
Repurchase of common stock			(45.1)	(28.7)
Cash dividend paid to stockholders			(21.0)	(19.1)
Intercompany loan			0.0	31.3
Net cash used in financing activities			(250.2)	(18.9)
Net (decrease) increase in cash and cash equivalents during the period			0.0	(5.0)
Cash and cash equivalents at beginning of period			0.0	5.0
Cash and cash equivalents 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			(140.8)	82.7
Cash flows from investing activities:
Capital expenditures			(26.0)	(38.1)
Purchase of available for sale securities			(0.5)	(53.4)
Proceeds from disposition of available for sale securities			84.0	82.2
Change in restricted cash				(0.7)
Net cash provided by (used in) investing activities			57.5	(10.0)
Cash flows from financing activities:
Repurchase of Senior Notes2			0.0
Settlement of Convertible Notes2			0.0
Proceeds from cash-settled call options related to settlement of Convertible Notes2			0.0
Payment for conversion premium related to settlement of Convertible Notes2			0.0
Excess tax benefit upon vesting of non-vested shares and dividend payment on unvested shares expected to vest			1.1	0.8
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 dividend paid to stockholders			0.0	0.0
Intercompany loan			(13.5)	(22.6)
Net cash used in financing activities			(12.4)	(21.8)
Net (decrease) increase in cash and cash equivalents during the period			(95.7)	50.9
Cash and cash equivalents at beginning of period			175.3	157.7
Cash and cash equivalents at end of period	79.6	208.6	79.6	208.6
Non-Guarantor Subsidiaries
Cash flows from operating activities:
Net cash provided by (used in) operating activities			(0.5)	7.1
Cash flows from investing activities:
Capital expenditures			(12.4)	(1.5)
Purchase of available for sale securities			0.0	0.0
Proceeds from disposition of available for sale securities			0.0	0.0
Change in restricted cash				0.0
Net cash provided by (used in) investing activities			(12.4)	(1.5)
Cash flows from financing activities:
Repurchase of Senior Notes2			0.0
Settlement of Convertible Notes2			0.0
Proceeds from cash-settled call options related to settlement of Convertible Notes2			0.0
Payment for conversion premium related to settlement of Convertible Notes2			0.0
Excess tax benefit upon vesting of non-vested shares and dividend payment on unvested shares expected to vest			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 dividend paid to stockholders			0.0	0.0
Intercompany loan			13.5	(8.7)
Net cash used in financing activities			13.5	(8.7)
Net (decrease) increase in cash and cash equivalents during the period			0.6	(3.1)
Cash and cash equivalents at beginning of period			2.4	6.8
Cash and cash equivalents at end of period	3.0	3.7	3.0	3.7
Consolidating Adjustments
Cash flows from operating activities:
Net cash provided by (used in) operating activities			0.0	0.0
Cash flows from investing activities:
Capital expenditures			0.0	0.0
Purchase of available for sale securities			0.0	0.0
Proceeds from disposition of available for sale securities			0.0	0.0
Change in restricted cash				0.0
Net cash provided by (used in) investing activities			0.0	0.0
Cash flows from financing activities:
Repurchase of Senior Notes2			0.0
Settlement of Convertible Notes2			0.0
Proceeds from cash-settled call options related to settlement of Convertible Notes2			0.0
Payment for conversion premium related to settlement of Convertible Notes2			0.0
Excess tax benefit upon vesting of non-vested shares and dividend payment on unvested shares expected to vest			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 dividend paid to stockholders			0.0	0.0
Intercompany loan			0.0	0.0
Net cash used in financing activities			0.0	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	$ 0.0	$ 0.0