Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted stock awards [Roll Forward]
Granted (in shares)					1,698,000	1,662,000	1,328,000
Vested (in shares)					(1,275,000)	(1,185,000)	(1,455,000)
Cancelled or forfeited (in shares)					(521,000)	(298,000)	(452,000)
Ending balance (in shares)	3,454,000				3,454,000	3,552,000	3,373,000	3,952,000
Weighted Average Grant Date Fair Value [Roll Forward]
Beginning balance (in dollars per share)				$ 25.70	$ 25.70	$ 21.12	$ 16.67
Granted (in dollars per share)					32.75	29.79	26.98
Vested (in dollars per share)					23.55	19.58	15.08
Cancelled/forfeited (in dollars per share)					18.68	21.02	18.87
Ending balance (in dollars per share)	$ 28.80				$ 28.80	$ 25.70	$ 21.12
Unrecognized compensation cost related to nonvested share-based compensation arrangements granted	$ 63,800				$ 63,800
Period over which cost is expected to be recognized					2 years 3 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares granted (in shares)					1,698,000	1,662,000	1,328,000
Percentage of estimated forfeitures, minimum					0.00%
Percentage of estimated forfeitures, maximum					20.00%
Restricted Stock [Member]
Restricted stock awards [Roll Forward]
Granted (in shares)	244,000	49,000	70,000	1,335,000
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares granted (in shares)	244,000	49,000	70,000	1,335,000
Value per share minimum (in dollars per share)	$ 21.82	$ 33.02	$ 36.12	$ 34.57
Value per share maximum (in dollars per share)	$ 21.82	$ 33.02	$ 36.12	$ 34.89
Total value of restricted shares granted	$ 5,327	$ 1,611	$ 2,540	$ 46,142
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage payroll deduction that each employee may deduct					15.00%
Percentage of closing market price paid for purchase of whole shares					90.00%
Number of shares reserved (in shares)	1,800,000				1,800,000