Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Weighted average stock options excluded (in shares)	0	0	15,531	0	7,389
Net Income
Basic income available to common stockholders	$ 27,303	$ 28,002	$ 14,176	$ 55,305	$ 23,697
Diluted income available to common stockholders plus assumed conversions	$ 27,303	$ 28,002	$ 14,176	$ 55,305	$ 23,697
Shares
Basic income available to common stockholders (in shares)	46,053,077	45,893,496	39,586,524	45,973,727	33,591,040
Dilutive effect of share-based compensation (in shares)	649,891	758,563	680,696	704,396	676,175
Diluted income available to common stockholders plus assumed conversions (in shares)	46,702,968	46,652,059	40,267,220	46,678,123	34,267,215
Per Share Amount
Basic income available to common stockholders (in dollars per share)	$ 0.59	$ 0.61	$ 0.36	$ 1.20	$ 0.71
Diluted income available to common stockholders plus assumed conversions (in dollars per share)	$ 0.58	$ 0.60	$ 0.35	$ 1.18	$ 0.69