Earnings Per Share (EPS Components) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Summary of earnings per share
Net income	$ 33,015	$ 23,852	$ 91,688	$ 65,140
Weighted Average Shares (in shares)
BASIC SHARES	27,537,841	27,436,792	27,517,210	27,242,902
EFFECT OF DILUTIVE SECURITIES	63,499	76,307	62,596	78,043
DILUTIVE SHARES	27,601,340	27,513,099	27,579,806	27,320,945
NET INCOME PER SHARE (in dollars per share)
BASIC EPS	$ 1.20	$ 0.87	$ 3.33	$ 2.39
EFFECT OF DILUTIVE SECURITIES	0	0	(0.01)	(0.01)
DILUTIVE EPS	$ 1.20	$ 0.87	$ 3.32	$ 2.38