Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share
Net income as reported	$ 7,529	$ 16,315	$ 11,955	$ 12,391	$ 13,628	$ 11,832	$ 12,352	$ 11,025	$ 48,190	$ 48,837	$ 38,450
Impact of assumed conversions
Weighted average common shares outstanding (in shares)									22,953,000	20,003,000	19,984,000
Additional dilutive common stock equivalents (in shares)									296,000	287,000	333,000
Weighted average diluted common shares outstanding (in shares)									23,249,000	20,290,000	20,317,000
Basic earnings per common share (in dollars per share)	$ 0.33	$ 0.70	$ 0.51	$ 0.57	$ 0.68	$ 0.59	$ 0.62	$ 0.55	$ 2.10	$ 2.44	$ 1.92
Diluted earnings per common share (in dollars per share)	$ 0.32	$ 0.69	$ 0.50	$ 0.56	$ 0.67	$ 0.59	$ 0.61	$ 0.54	$ 2.07	$ 2.41	$ 1.89
Common stock equivalents excluded from earnings per share calculations due to anti-dilutive effect (in shares)									0	0	79,670
Convertible Debt Securities
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Convertible trust preferred securities, interest rate, stated percentage	9.00%				9.00%				9.00%	9.00%	9.00%