Stock-Based Compensation (RSU Activity) (Details)	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
RSUs
Number of Shares
Balance at the beginning of the period (in shares) | shares	964,000
Granted (in shares) | shares	503,000
Vested (in shares) | shares	(383,000)
Cancelled (in shares) | shares	(123,000)
Balance at the end of the period (in shares) | shares	961,000
Weighted-Average Grant Date Fair Value
Balance at the beginning of the period (in dollars per share) | $ / shares	$ 28.25
Granted (in dollars per share) | $ / shares	33.34
Vested (in dollars per share) | $ / shares	28.32
Cancelled (in dollars per share) | $ / shares	30.12
Balance at the end of the period (in dollars per share) | $ / shares	$ 30.64
Restricted Stock | Outside directors
Number of Shares
Granted (in shares) | shares	1,460
Weighted-Average Grant Date Fair Value
Granted (in dollars per share) | $ / shares	$ 34.20
Additional Disclosure
Grant-date fair value (in dollars) | $	$ 50,000