Equity Incentive Plans (Restricted Stock Activity) (Details) - Restricted Stock Award $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Summary of the activity of restricted stock
Restricted stock outstanding shares, Beginning Balance | shares	1,345
Granted shares | shares	933
Vested shares | shares	(442)
Forfeited/canceled shares | shares	(66)
Restricted stock outstanding shares, Ending Balance | shares	1,770
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Restricted stock outstanding Wtd. Avg. Grant Date Fair Value, Beginning Balance (in dollars per share) | $ / shares	$ 24.37
Granted Wtd. Avg. Grant Date Fair Value (in dollars per share) | $ / shares	35.31
Vested Wtd. Avg. Grant Date Fair Value (in dollars per share) | $ / shares	23.23
Forfeited/Canceled Wtd. Avg. Grant Date Fair Value (in dollars per share) | $ / shares	26.89
Restricted stock outstanding Wtd. Avg. Grant Date Fair Value, Ending Balance (in dollars per share) | $ / shares	$ 30.47
Unrecognized compensation costs related to awards | $	$ 33.4
Expected weighted average period to recognize expense	2 years 6 months