Earnings Per Share (Basic and Diluted EPS) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Income attributable to common stockholders	$ 35,858	$ 18,443	$ 91,622	$ 39,783
Weighted average common shares outstanding, basic (in shares)	67,329	66,958	67,246	66,860
Weighted average common shares outstanding, diluted (in shares)	67,896	67,442	67,743	67,341
Basic income per common share (in dollars per share)	$ 0.53	$ 0.28	$ 1.36	$ 0.60
Diluted income per common share (in dollars per share)	$ 0.53	$ 0.27	$ 1.35	$ 0.59
Restricted stock units [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Stock based payment arrangements (in shares)	399	248	321	212
Stock options [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Stock based payment arrangements (in shares)	166	175	155	201
Restricted stock [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Stock based payment arrangements (in shares)	2	61	21	68