Reconciliation of BEPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Reconciliation of basic earnings per share ("EPS") to diluted EPS
Net income available to common stockholders	$ 26,201	$ 21,509	$ 42,544	$ 36,328	$ 31,560
Basic weighted-average shares outstanding (in shares)	48,399	49,254	48,353		49,236
Dilutive effect of potential common stock equivalents — stock options and restricted stock units (in shares)	206	219	180		209
Diluted weighted-average shares outstanding (in shares)	48,605	49,473	48,533		49,445
Earnings per common share:
Basic (in dollars per share)	$ 0.54	$ 0.44	$ 0.88		$ 0.64
Diluted (in dollars per share)	$ 0.54	$ 0.43	$ 0.88		$ 0.64
Potentially dilutive securities excluded from earnings per diluted share because their effect is anti-dilutive	0	0	0		0