Performance Incentive Plan (Restricted Stock Activity) (Details)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Number of Shares
Restricted shares granted (in shares) | shares	40,581
Weighted Average Share Price
Restricted shares granted (in dollars per share) | $ / shares	$ 41.84
Restricted stock
Number of Shares
Non-vested restricted shares, January 1 (in shares) | shares	735,323
Restricted shares granted (in shares) | shares	291,281
Restricted shares vested (in shares) | shares	(175,243)
Restricted shares forfeited (in shares) | shares	(67,153)
Restricted shares repurchased (in shares) | shares	(2,644)
Non-vested restricted shares, December 31 (in shares) | shares	781,564
Weighted Average Share Price
Non-vested restricted shares, January 1 (in dollars per share) | $ / shares	$ 42.65
Restricted shares granted (in dollars per share) | $ / shares	37.06
Restricted shares vested (in dollars per share) | $ / shares	40.43
Restricted shares forfeited (in dollars per share) | $ / shares	41.00
Restricted shares repurchased (in dollars per share) | $ / shares	40.43
Non-vested restricted shares, December 31 (in dollars per share) | $ / shares	$ 41.21