- Shares and EPS (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 series	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 1999 rightpershare
Common Stock
Number of votes for each share of common stock held									1
Number of rights per common stock as a part of dividend distribution												1
Percentage acquisition of common stock triggering exercise terms of rights, minimum									15.00%
Ownership interest held by any stockholder at date of rights distribution to which additional exercise terms for the Rights distributed apply (as a percent)									25.00%
Subsequent increase in ownership interest held by any stockholder after rights distribution to which additional exercise terms for the Rights distributed apply (as a percent)									40.00%
Redemption price per right (in cents per right)									$ 0.01
Preferred Stock
Number of series by which the Board may issue authorized and unissued preferred stock, minimum									1
Reconciliation of basic earnings per share ("EPS") to diluted EPS
Net income available to common stockholders	$ 10,380	$ 20,614	$ 20,451	$ 12,086	$ 7,668	$ 20,006	$ 18,502	$ 4,795	$ 63,531	$ 50,971	$ 41,918
Basic weighted-average shares outstanding									48,977	48,521	48,339
Dilutive effect of potential common stock equivalents - stock options (in shares)									217	152	73
Diluted weighted-average shares outstanding									49,194	48,673	48,412
Net earnings per share:
Basic (in dollars per share)	$ 0.21	$ 0.42	$ 0.42	$ 0.25	$ 0.16	$ 0.41	$ 0.38	$ 0.10	$ 1.30	$ 1.05	$ 0.87
Diluted (in dollars per share)	$ 0.21	$ 0.42	$ 0.42	$ 0.25	$ 0.16	$ 0.41	$ 0.38	$ 0.10	$ 1.29	$ 1.05	$ 0.87
Potentially dilutive securities excluded from earnings per diluted share because their effect is anti-dilutive (in shares)									0	0	1,700