Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Weighted average stock options excluded (in shares)	0	0	10,036	7,530	12,192
Net Income
Basic income available to common stockholders	$ 28,392	$ 27,303	$ 20,232	$ 83,697	$ 43,929
Diluted income available to common stockholders plus assumed conversions	$ 28,392	$ 27,303	$ 20,232	$ 83,697	$ 43,929
Shares
Basic income available to common stockholders (in shares)	61,727,030	46,053,077	39,709,565	51,282,533	35,652,626
Dilutive effect of share-based compensation (in shares)	634,774	649,891	776,549	683,114	803,319
Diluted income available to common stockholders plus assumed conversions (in shares)	62,361,804	46,702,968	40,486,114	51,965,647	36,455,945
Per Share Amount
Basic income available to common stockholders (in dollars per share)	$ 0.46	$ 0.59	$ 0.51	$ 1.63	$ 1.23
Diluted income available to common stockholders plus assumed conversions (in dollars per share)	$ 0.46	$ 0.58	$ 0.50	$ 1.61	$ 1.20