Earnings Per Share - Reconciliation of Numerators and Denominators of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended									12 Months Ended
		Sep. 11, 2018	Dec. 31, 2019		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 10, 2018
Numerator for Earnings per Common Share-Basic:
Net Income												$ 98,234	$ 105,334	$ 72,968
Less: Income allocated to participating shares												260	304	242
Net Income Allocated to Common Shareholders			$ 22,269	[1]	$ 26,936	$ 26,101	$ 22,928	$ 26,854	$ 30,881	$ 21,436	$ 26,163	97,974	105,030	72,726
Numerator for Earnings per Common Share—Diluted:
Net Income												$ 98,234	$ 105,334	$ 72,968
Denominators:
Weighted Average Common Shares Outstanding-Basic (in shares)												34,628,191	34,775,784	34,729,376
Add: Dilutive potential common shares (in shares)												94,763	199,625	225,391
Denominator for Treasury Stock Method-Diluted (in shares)												34,722,954	34,975,409	34,954,767
Weighted Average Common Shares Outstanding-Basic (in shares)												34,628,191	34,775,784	34,729,376
Add: Average participating shares outstanding (in shares)												51,287	100,733	115,418
Denominator for Two-Class Method-Diluted (in shares)												34,679,478	34,876,517	34,844,794
Earnings per common share—basic (in USD per share)												$ 2.84	$ 3.03	$ 2.10
Earnings per common share—diluted (in USD per share)			$ 0.62	[1]	$ 0.79	$ 0.76	$ 0.66	$ 0.77	$ 0.88	$ 0.61	$ 0.75	$ 2.82	$ 3.01	$ 2.09
Repurchase of warrant		$ 7,700										$ 0	$ 7,652	$ 0
Number of shares of common stock that holder of warrants have right to purchase (in shares)															517,012
Warrants exercise price (in USD per share)			$ 31.53					$ 31.53				$ 31.53	$ 31.53	$ 31.53	$ 31.53
Warrants
Denominators:
Anti-dilutive securities excluded from dilutive potential common shares	[2]											0	267,106	438,681
Restricted Stock
Denominators:
Anti-dilutive securities excluded from dilutive potential common shares												12,686	81,587	88,578

[1] The DNB Merger is included in our consolidated financial statements beginning on December 1, 2019.

[2] We repurchased our outstanding warrant on September 11, 2018 for $7.7 million. Prior to the repurchase, the warrant provided the holder the right to 517,012 shares of common stock at a strike price of $31.53 per share via cashless exercise.