Earnings Per Share (Details) - USD ($) $ / shares in Units, $ 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
Antidilutive Securities Excluded from Computation of Earnings Per Share
Net income as reported	$ 23,529	$ 22,516	$ 22,251	$ 20,921	$ 7,529	$ 16,315	$ 11,955	$ 12,391	$ 89,217	$ 48,190	$ 48,837
Impact of assumed conversions
Weighted average common shares outstanding (in shares)									23,100,000	22,953,000	20,003,000
Additional dilutive common stock equivalents (in shares)									189,000	296,000	287,000
Weighted average diluted common shares outstanding (in shares)									23,289,000	23,249,000	20,290,000
Basic earnings per common share (in dollars per share)	$ 1.02	$ 0.97	$ 0.96	$ 0.91	$ 0.33	$ 0.70	$ 0.51	$ 0.57	$ 3.86	$ 2.10	$ 2.44
Diluted earnings per common share (in dollars per share)	$ 1.02	$ 0.97	$ 0.95	$ 0.90	$ 0.32	$ 0.69	$ 0.50	$ 0.56	$ 3.83	$ 2.07	$ 2.41
Common stock equivalents excluded from earnings per share calculations due to anti-dilutive effect (in shares)									0	0
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%