Net Income Per Share - Reconciliation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Net Income
Net income available to common stockholders	$ 23,193	$ 17,693
Diluted net income per share	$ 23,193	$ 17,693
Weighted-Average Shares
Net income available to common stockholders (in shares)	40,984,481	40,690,573
Effect of dilutive stock options and warrants (in shares)	236,105	226,399
Diluted net income per share (in shares)	41,220,586	40,916,972
Per Share Amount
Net income available to common stockholders (in dollars per share)	$ 0.57	$ 0.43
Diluted net income per share (in dollars per share)	$ 0.56	$ 0.43