Consolidated Statement of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands		Total	Common stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income
Balance, beginning of year (in shares) at Dec. 31, 2017			24,916,806
Beginning Balance at Dec. 31, 2017		$ 973,373	$ 25	$ 196,334	$ 608,700	$ 168,314
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		45,759			45,759
Shares repurchased (in shares)			(120,372)
Shares repurchased		(5,404)		(5,404)
Stock based compensation (in shares)			116,314
Stock based compensation		3,574		3,574
Dividends on common stock		(6,958)			(6,958)
Change in net unrealized investment appreciation	[1]	(40,962)			(6,714)	(34,248)
Change in liability for underfunded employee benefit plans	[2]	1,311				1,311
Balance, end of year (in shares) at Mar. 31, 2018			24,912,748
Ending Balance at Mar. 31, 2018		970,693	$ 25	194,504	832,031	(55,867)
Balance, beginning of year (in shares) at Dec. 31, 2017			24,916,806
Beginning Balance at Dec. 31, 2017		973,373	$ 25	196,334	608,700	168,314
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		56,986
Balance, end of year (in shares) at Sep. 30, 2018			25,066,384
Ending Balance at Sep. 30, 2018		884,216	$ 25	201,361	752,581	(69,751)
Balance, beginning of year (in shares) at Mar. 31, 2018			24,912,748
Beginning Balance at Mar. 31, 2018		970,693	$ 25	194,504	832,031	(55,867)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		157			157
Stock based compensation (in shares)			131,219
Stock based compensation		4,938		4,938
Dividends on common stock		(7,757)			(7,757)
Change in net unrealized investment appreciation	[1]	(4,743)				(4,743)
Change in liability for underfunded employee benefit plans	[2]	1,312				1,312
Balance, end of year (in shares) at Jun. 30, 2018			25,043,967
Ending Balance at Jun. 30, 2018		964,600	$ 25	199,442	824,431	(59,298)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		11,070			11,070
Stock based compensation (in shares)			22,417
Stock based compensation		1,919		1,919
Dividends on common stock		(82,920)			(82,920)
Change in net unrealized investment appreciation	[1]	(11,765)				(11,765)
Change in liability for underfunded employee benefit plans	[2]	1,312				1,312
Balance, end of year (in shares) at Sep. 30, 2018			25,066,384
Ending Balance at Sep. 30, 2018		$ 884,216	$ 25	201,361	752,581	(69,751)
Balance, beginning of year (in shares) at Dec. 31, 2018		25,097,408	25,097,408
Beginning Balance at Dec. 31, 2018		$ 888,375	$ 25	203,350	715,472	(30,472)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		44,521			44,521
Stock based compensation (in shares)			70,414
Stock based compensation		3,438		3,438
Dividends on common stock		(7,797)			(7,797)
Change in net unrealized investment appreciation	[1]	26,279				26,279
Change in liability for underfunded employee benefit plans	[2]	888				888
Balance, end of year (in shares) at Mar. 31, 2019			25,167,822
Ending Balance at Mar. 31, 2019		$ 955,191	$ 25	206,788	751,683	(3,305)
Balance, beginning of year (in shares) at Dec. 31, 2018		25,097,408	25,097,408
Beginning Balance at Dec. 31, 2018		$ 888,375	$ 25	203,350	715,472	(30,472)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		$ 37,983
Balance, end of year (in shares) at Sep. 30, 2019		25,081,726	25,081,726
Ending Balance at Sep. 30, 2019		$ 964,168	$ 25	202,504	728,536	33,103
Balance, beginning of year (in shares) at Mar. 31, 2019			25,167,822
Beginning Balance at Mar. 31, 2019		955,191	$ 25	206,788	751,683	(3,305)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		(4,196)			(4,196)
Shares repurchased (in shares)			(1,507)
Shares repurchased		(69)		(69)
Stock based compensation (in shares)			78,885
Stock based compensation		2,252		2,252
Dividends on common stock		(8,325)			(8,325)
Change in net unrealized investment appreciation	[1]	22,562				22,562
Change in liability for underfunded employee benefit plans	[2]	888				888
Balance, end of year (in shares) at Jun. 30, 2019			25,245,200
Ending Balance at Jun. 30, 2019		968,303	$ 25	208,971	739,162	20,145
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		(2,342)			(2,342)
Shares repurchased (in shares)			(177,249)
Shares repurchased		(8,058)		(8,058)
Stock based compensation (in shares)			13,775
Stock based compensation		1,591		1,591
Dividends on common stock		(8,284)			(8,284)
Change in net unrealized investment appreciation	[1]	12,070				12,070
Change in liability for underfunded employee benefit plans	[2]	$ 888				888
Balance, end of year (in shares) at Sep. 30, 2019		25,081,726	25,081,726
Ending Balance at Sep. 30, 2019		$ 964,168	$ 25	$ 202,504	$ 728,536	$ 33,103

[1] The change in net unrealized appreciation is net of reclassification adjustments and income taxes.

[2] The change in liability for underfunded employee benefit plans is net of reclassification adjustments and income taxes.