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, 2015		2,000	24,649,044
Stockholders' Equity, Beginning Balance at Dec. 31, 2015	$ 596,566	$ 48,163	$ 271	$ 241,239	$ 355,427	$ (48,534)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	56,609				56,609
Dividends declared to preferred shareholders	(4,875)				(4,875)
Common share issuance for conversion of convertible notes - shares			0
Common share issuance for conversion of convertible notes - value	269		$ 0	269
Stock options exercised - shares			14,600
Stock options exercised - value	182			(108)		290
Stock-based compensation expense	5,315			5,315
Deferral of executive and director compensation	108			108
Executive and director deferred compensation distributions - shares			13,789
Executive and director deferred compensation distributions - value	0			(274)		274
Shares Outstanding, Ending Balance at Dec. 31, 2016		2,000	24,677,433
Stockholders' Equity, Ending 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	0	$ 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
Executive and director deferred compensation distributions - shares			84,635
Executive and director deferred compensation distributions - value	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		(1,069,043)
Treasury Stock, Value, Acquired, Cost Method	$ (25,709)					(25,709)
Stock options exercised - shares	(38,628)		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
Executive and director deferred compensation distributions - shares			61,366
Executive and director deferred compensation distributions - value	(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)