Earnings Per Share - Factors Used in Computation of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Basic
Net income to common stockholders	$ 22,005	$ 14,317	$ 30,995	$ 41,835
Weighted average common shares outstanding (in shares)	24,592,092	25,621,054	24,298,897	26,228,499
Basic earnings per common share (in dollars per share)	$ 0.89	$ 0.56	$ 1.28	$ 1.60
Diluted
Net income to common stockholders	$ 22,005	$ 14,317	$ 30,995	$ 41,835
Weighted average common shares outstanding (in shares)	24,592,092	25,621,054	24,298,897	26,228,499
Dilutive effects of:
Average shares and dilutive potential common shares (in shares)	24,802,388	25,734,471	24,464,215	26,331,740
Diluted earnings per common share (in dollars per share)	$ 0.89	$ 0.56	$ 1.27	$ 1.59
Stock Options
Dilutive effects of:
Stock based compensation (in shares)	48,102	60,068	53,232	61,054
Restricted stock awards
Dilutive effects of:
Stock based compensation (in shares)	67,907	45,631	65,893	40,572
Restricted stock units
Dilutive effects of:
Stock based compensation (in shares)	18,192	3,045	15,198	57
Performance stock units - market based
Dilutive effects of:
Stock based compensation (in shares)	76,095	4,673	30,995	1,558
Performance stock units - performance based
Dilutive effects of:
Stock based compensation (in shares)	0	0	0	0