Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Basic earnings per share [Abstract]
Net income available to common shareholders	$ 75,074us-gaap_NetIncomeLoss	$ 61,747us-gaap_NetIncomeLoss	$ 54,558us-gaap_NetIncomeLoss
Weighted average common shares, basic (in shares)	43,877,000	41,930,000	33,379,000
Basic EPS (in dollars per share)	$ 1.71us-gaap_EarningsPerShareBasic	$ 1.47us-gaap_EarningsPerShareBasic	$ 1.63us-gaap_EarningsPerShareBasic
Diluted earnings per share [Abstract]
Net income available to common shareholders	$ 75,074us-gaap_NetIncomeLoss	$ 61,747us-gaap_NetIncomeLoss	$ 54,558us-gaap_NetIncomeLoss
Dilutive effect of stock based compensation (in shares)	518,000	420,000	340,000
Weighted average common shares, diluted (in shares)	44,395,000	42,350,000	33,719,000
Diluted EPS (in dollars per share)	$ 1.69us-gaap_EarningsPerShareDiluted	$ 1.46us-gaap_EarningsPerShareDiluted	$ 1.62us-gaap_EarningsPerShareDiluted
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock options excluded from calculation of diluted EPS (in shares)	493,000	1,048,000	1,193,000

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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