Stock-Based Compensation (RSU Activity) (Details)	9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares
RSUs
Number of Shares
Balance at the beginning of the period (in shares) | shares	871,000
Granted (in shares) | shares	572,000
Vested (in shares) | shares	(367,000)
Cancelled (in shares) | shares	(90,000)
Balance at the end of the period (in shares) | shares	986,000
Weighted-Average Grant Date Fair Value
Balance at the beginning of the period (in dollars per share) | $ / shares	$ 28.42
Granted (in dollars per share) | $ / shares	28.24
Vested (in dollars per share) | $ / shares	28.59
Cancelled (in dollars per share) | $ / shares	28.30
Balance at the end of the period (in dollars per share) | $ / shares	$ 28.26
Restricted Stock | Outside directors
Number of Shares
Granted (in shares) | shares	4,820
Weighted-Average Grant Date Fair Value
Granted (in dollars per share) | $ / shares	$ 31.09
Additional Disclosure
Grant-date fair value (in dollars) | $	$ 150,000