Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Basic and Diluted Earnings Per Share
Net Income		$ 81,860	$ 77,757	$ 63,444	$ 43,339	$ 57,410	$ 51,610	$ 52,392	$ 49,132	$ 266,400	$ 210,544	$ 181,878
Average outstanding shares - basic (in shares)										94,883,864	88,255,290	83,603,515
Add: dilutive restricted stock units and stock options (in shares)										48,489	130,485	73,670
Average outstanding shares - diluted (in shares)										94,932,353	88,385,775	83,677,185
Basic earnings per share (in dollars per share)		$ 0.86	$ 0.81	$ 0.67	$ 0.46	$ 0.62	$ 0.57	$ 0.61	$ 0.58	$ 2.81	$ 2.39	$ 2.18
Diluted earnings per share (in dollars per share)		$ 0.86	$ 0.81	$ 0.66	$ 0.46	$ 0.62	$ 0.57	$ 0.61	$ 0.58	$ 2.81	$ 2.38	$ 2.17
Restricted stock units and stock options excluded from the diluted average outstanding share calculation (in shares)	[1]									88,240	0	1,357

[1] Anti-dilution occurs when the unrecognized compensation cost per share of a restricted stock units or the exercise price of a stock option exceeds the market price of the Company’s stock.