Earnings per Share Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income									$ 56,609	$ 51,763	$ 50,789
Preferred dividends									(4,875)	(4,875)	(4,875)
Net Income Available to Common Stockholders	$ 19,343	$ 9,724	$ 14,697	$ 7,970	$ 12,056	$ 14,352	$ 12,131	$ 8,349	51,734	46,888	45,914
Net income available to common shareholders									$ 55,304	$ 50,408	$ 49,448
Basic Weighted Average Shares Outstanding	24,671	24,669	24,669	24,657	24,649	24,605	24,531	24,514	24,666	24,575	24,463
Stock option awards									216	237	222
Deferred compensation awards										150	142
Diluted Weighted Average Shares Outstanding	30,166	30,139	30,077	30,032	30,107	30,067	30,023	29,975	30,116	30,047	29,912
Earnings Per Share, Basic	$ 0.78	$ 0.39	$ 0.60	$ 0.32	$ 0.49	$ 0.58	$ 0.49	$ 0.34	$ 2.10	$ 1.91	$ 1.88
Earnings Per Share, Diluted	$ 0.67	$ 0.35	$ 0.52	$ 0.30	$ 0.43	$ 0.51	$ 0.43	$ 0.31	$ 1.84	$ 1.68	$ 1.65
Anti-dilutive stock equivalent awards not included in the calculation of diluted loss per share									1,273	1,447	1,250
2018 Convertible Senior Notes [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Interest on 3.25% convertible senior subordinated notes due 2017									$ 2,050	$ 2,021	$ 2,030
Convertible senior subordinated notes potential shares									2,669	2,669	2,669
2017 Convertible Senior Notes [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Interest on 3.25% convertible senior subordinated notes due 2017									$ 1,520	$ 1,499	$ 1,504
Convertible senior subordinated notes potential shares									2,416	2,416	2,416