Consolidated Statement of Shareholders' Equity - USD ($) $ in Thousands	Total	Preferred Shares [Member]	Common Shares [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Shares [Member]
Shares Outstanding, Beginning Balance at Dec. 31, 2016		2,000	24,677,433
Stockholders' Equity, Beginning Balance at Dec. 31, 2016	$ 654,174	$ 48,163	$ 271	$ 246,549	$ 407,161	$ (47,970)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	72,081				72,081
Fair value over carrying value of preferred share redeemed		$ 2,257			(2,257)
Dividends declared to preferred shareholders	(3,656)				(3,656)
Common share issuance for conversion of convertible notes - shares			2,415,903
Common share issuance for conversion of convertible notes - value	57,500		$ 24	57,476
Preferred shares redeemed - shares		(2,000)
Preferred shares redeemed - value	(50,420)	$ (50,420)
Stock options exercised - shares			678,781
Stock options exercised - value	11,225			(2,255)		13,480
Stock-based compensation expense	6,044			6,044
Deferral of Executive and Director Compensation	350			350
Deferred Compensation Arrangement with Individual, Shares Issued		0	84,635
Deferred Compensation Arrangement with Individual, Distribution Paid	0			(1,681)		1,681
Shares Outstanding, Ending Balance at Dec. 31, 2017		0	27,856,752
Stockholders' Equity, Ending Balance at Dec. 31, 2017	747,298	$ 0	$ 295	306,483	473,329	(32,809)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	107,663				107,663
Common share issuance for conversion of convertible notes - shares		0	628,515
Common share issuance for conversion of convertible notes - value	20,309	$ 0	$ 6	20,303	0	0
Treasury Stock, Shares, Acquired			(1,069,043)
Treasury Stock, Value, Acquired, Cost Method	(25,709)					(25,709)
Stock options exercised - shares			38,628
Stock options exercised - value	538			(254)		792
Stock-based compensation expense	5,974			5,974
Deferral of Executive and Director Compensation	185			185
Deferred Compensation Arrangement with Individual, Shares Issued		0	61,366
Deferred Compensation Arrangement with Individual, Distribution Paid	(955)			(2,174)		1,219
Shares Outstanding, Ending Balance at Dec. 31, 2018		0	27,516,218
Stockholders' Equity, Ending Balance at Dec. 31, 2018	855,303	$ 0	$ 301	330,517	580,992	(56,507)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 127,587				127,587
Treasury Stock, Shares, Acquired	200,000		(201,088)
Treasury Stock, Value, Acquired, Cost Method	$ (5,150)					(5,150)
Stock options exercised - shares	(954,370)		954,370
Stock options exercised - value	$ 19,644			(1,204)		20,848
Stock-based compensation expense	5,846			5,846
Deferral of Executive and Director Compensation	247			247
Deferred Compensation Arrangement with Individual, Shares Issued		0	116,956
Deferred Compensation Arrangement with Individual, Distribution Paid	0			(2,545)		2,545
Shares Outstanding, Ending Balance at Dec. 31, 2019		0	28,386,456
Stockholders' Equity, Ending Balance at Dec. 31, 2019	$ 1,003,477	$ 0	$ 301	$ 332,861	$ 708,579	$ (38,264)