Earnings per Share Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income									$ 107,663	$ 72,081	$ 56,609
Preferred dividends									0	(3,656)	(4,875)
Excess of fair value over book value of preferred shares redeemed									0	(2,257)	0
Net Income Available to Common Stockholders	$ 32,407	$ 29,282	$ 27,911	$ 18,063	$ 15,882	$ 18,852	$ 15,770	$ 15,664	107,663	66,168	51,734
Diluted income available to common shareholders									$ 108,070	$ 69,387	$ 55,304
Basic Weighted Average Shares Outstanding	27,774	28,469	28,571	28,124	27,736	25,581	24,990	24,738	28,234	25,769	24,666
Stock option awards									295	342	216
Deferred compensation awards									219	221	149
Diluted Weighted Average Shares Outstanding	28,181	28,906	29,101	30,544	31,172	30,675	30,619	30,329	29,178	30,688	30,116
Earnings Per Share, Basic	$ 1.17	$ 1.03	$ 0.98	$ 0.64	$ 0.57	$ 0.74	$ 0.63	$ 0.63	$ 3.81	$ 2.57	$ 2.10
Earnings Per Share, Diluted	$ 1.15	$ 1.01	$ 0.96	$ 0.60	$ 0.53	$ 0.64	$ 0.55	$ 0.55	$ 3.70	$ 2.26	$ 1.84
Anti-dilutive stock equivalent awards not included in the calculation of diluted loss per share									381	23	1,273
2018 Convertible Senior Notes [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Interest on convertible senior subordinated notes									$ 407	$ 2,113	$ 2,050
Convertible senior subordinated notes potential shares									430	2,669	2,669
2017 Convertible Senior Notes [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Interest on convertible senior subordinated notes									$ 0	$ 1,106	$ 1,520
Convertible senior subordinated notes potential shares									0	1,687	2,416